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Term of the Month

Defining Criminal Justice Research

Welcome to NIJ’s Term of the Month. Each month we are featuring a term from our scientific research portfolios informing significant American justice system issues and solutions.

July 2024 — Short Tandem Repeats

DNA is made up of four bases, known collectively as C, T, A, and G. These bases are arranged in long strings which pair together to create double strand DNA. Short tandem repeats (STRs) are DNA sequences that can be used to identify people. Specifically, STRs are multiple copies of an identical (or similar) DNA sequence arranged in direct succession where the repeat sequence unit is two base pairs to six base pairs in length.[1]  By looking at the number of repeat segments across multiple areas of the DNA, investigators can determine whether a DNA profile is unique and, therefore, able to identify an individual.

Current estimates indicate that 1%-3% of DNA is the same in all people. This percentage of DNA acts the same for everybody: it encodes precise, universal proteins that define us as healthy humans. However, in the other 97%-99%, the DNA sequence does not create important proteins or do anything else of genetic importance that we recognize. STRs occur in these areas; because they have no known functional effect, they vary greatly from person to person.

By comparing STRs, forensic investigators can use DNA to distinguish among individuals. In one person, for example, there could be a five-repeat sequence of CTAG. At the same site on another person’s DNA, the CTAG sequence could repeat six or seven times. The variation among individuals is enormous, making it useful for identification.

When collecting DNA evidence in forensic investigations of a crime, the FBI has designated 20 of the most common STR loci (specific DNA regions) to serve as the standard for its Combined DNA Index System (CODIS). CODIS is a database containing DNA profiles from persons convicted of or arrested for crimes, unsolved crime scene evidence, and missing persons. The combination of STRs across the 20 loci vary tremendously. Each unique combination creates an individual DNA profile. This means CODIS examines millions of possible STR combinations when investigators are looking for a DNA match. Because of these myriad combinations, the odds of finding a match (match rarity) in the 20 loci is at least 1 in 14 million and is often much higher. By establishing the 20 STR loci standard, the FBI system ensures that all forensic laboratories have a uniform database for using and sharing information.

This uniformity makes DNA matching more efficient, and it also means that STRs can potentially resolve more than one case. When DNA evidence is collected at a crime scene or from a victim of a crime, a DNA profile is developed and entered into CODIS. A CODIS search is then performed and can result in two types of associations. The first is with a DNA profile from another crime and the second is with a DNA profile from a convicted or arrested individual. This provides two types of investigative leads, one connecting the crime scene sample to another crime scene and the other to a convicted person. The result provides information that has the potential to either connect cases to each other or a case to an individual.

Reading and Resources


[note 1] “ANSI/ASB 022 Standard for Forensic DNA Analysis Training Programs, First Edition” AAFS Academy Standards Board (ASB), 2019, https://www.aafs.org/asb-standard/standard-forensic-dna-analysis-training-programs.


Financial fraud occurs when a persons obtains the voluntary provision of personal information, property, or monetary resources through the use of duplicitous tactics. For an incident to be classified as a personal financial fraud, victims must be intentionally deceived and lose money in the transaction.

Financial fraud of older adults (persons age 60 or older [1]) falls under the larger category of financial exploitation, which includes improper use of another person’s funds, property, or resources. Financial exploitation also includes financial abuse. The primary distinction between financial abuse and financial fraud is who commits the crime. Individuals who know the victim and are in positions of trust (for example, family members or paid caregivers) commit financial abuse of older adults; strangers mainly commit financial fraud.[2]

Research has found that older adults are more likely to be targets of fraud than younger adults.[3] Changes in the aging brain and declines in cognitive functioning (ranging from mild impairments to Alzheimer’s disease and dementia) make older adults more susceptible to scams and fraud.[4] Other risk factors include a lack of financial literacy,[5] social isolation, and loneliness.[6]

The consequences of financial fraud victimization may also be more severe for older adults than younger adults. Research has found that they lose more money, on average, than younger victims.[7] According to the Better Business Bureau, older adults lose more than $36 billion to financial fraud every year.[8] The actual number of fraud cases is unknown as many people do not report their victimization, and underreporting is especially high for older adults.[9]

Reading and Resources


[note 1] Ages of older adults in the research range from a low of 50 (AARP) to a high of 65 (Census). Here we define older adults as persons aged 60 or older. This is consistent with the Elder Abuse Prevention and Prosecution Act of 2017 and Older Americans Act of 1965 [42 USC §3002(38)].

[note 2] David Burnes et al., “Prevalence of Financial Fraud and Scams Among Older Adults in the United States: A Systematic Review and Meta-Analysis,” American Journal of Public Health 107 no. 8 (2017): 1193-1340, https://doi.org/10.2105/AJPH.2017.303821; and Marti DeLiema, “Fraud Versus Financial Abuse and the Influence of Social Relationships,” National Adult Protective Services Association, Research to Practice Series, 2018, https://www.napsa-now.org/wp-content/uploads/2012/06/Fraud-versus-financial-abuse-and-the-influence-of-social-relationships.pdf.

[note 3] Joanna Bieda and Soo Park, “Affluent Senior Citizens and Telemarketing Fraud,” Journal of Student Research 10 no. 1 (2021): 1-10, https://doi.org/10.47611/jsrhs.v10i1.1408.

[note 4] Burnes et al., “Prevalence of Financial Fraud and Scams”; and R. Nathan Spreng et al., “Aging and Financial Exploitation Risk,” in Aging and Money, 2nd ed., ed. Ronan M. Factora (Springer, 2021), 55-73, https://doi.org/10.1007/978-3-030-67565-3_5.

[note 5] Michael S. Finke, John S. Howe, and Sandra J. Huston, “Old Age and the Decline in Financial Literacy,” Management Science 63 no. 1 (2016): 213-230, https://doi.org/10.1287/mnsc.2015.2293.

[note 6] Marti DeLiema, “Fraud Versus Financial Abuse and the Influence of Social Relationships,” National Adult Protective Services Association, Research to Practice Series, 2018, https://www.napsa-now.org/wp-content/uploads/2012/06/Fraud-versus-financial-abuse-and-the-influence-of-social-relationships.pdf.

[note 7] Federal Trade Commission, Protecting Older Consumers 2021-2022: A Report of the Federal Trade Commission, Washington, DC: Federal Trade Commission, 2022, https://www.ftc.gov/system/files/ftc_gov/pdf/P144400OlderConsumersReportFY22.pdf.

[note 8] American Advisors Group (AAG), “AAG and Better Business Bureau Expand Fight Against Senior Targeted Financial Fraud,” March 21, 2019, Cision, https://www.prnewswire.com/news-releases/aag-and-better-business-bureau-expand-fight-against-senior-targeted-financial-fraud-300816638.html.

[note 9] Jingjin Shao et al., “Why Are Older Adults Victims of Fraud? Current Knowledge and Prospects Regarding Older Adults’ Vulnerability to Fraud,” Journal of Elder Abuse & Neglect 31 no. 3 (2019): 225-243, https://doi.org/10.1080/08946566.2019.1625842.

In forensics, user-generated recordings are audio or video recordings taken on devices such as smartphones, body worn cameras, or surveillance cameras. These recordings provide firsthand accounts of events during investigations. They often supply key evidence in investigations and legal proceedings, helping corroborate facts and reconstruct timelines for thefts, assaults, homicides, and other cases.  

Because user-generated recordings can be modified, an audio or video forensic examiner should establish their validity. Recordings often contain background noise from wind or traffic that is removed by algorithms in the device itself. Audio forensic examiners can assess whether a recording is intact or if it has been modified beyond changes commonly made by the device. An examiner can also filter out competing sounds and isolate audio of interest. If there are multiple recordings of the same event, examiners may be able to time synchronize audio files and determine the approximate positions of the microphones.

Forensic analyses also must advance to keep pace with the development of new and sophisticated AI deepfakes. 

Reading and Resources

The strength of our criminal justice system depends on its ability to convict people who have committed crimes and to clear those who are innocent. We have been refining this system for more than 200 years and dedicated public servants strive to keep us safe, bring justice and a sense of closure to victims, and defend the rights of individuals accused of crimes.  

But innocent people are sometimes wrongfully convicted. The conviction of a person for a crime that they did not commit is one of the greatest travesties of the criminal justice system.

People who are innocent are sometimes convicted of crimes committed by others (wrong person cases) or are found guilty even though a crime was not committed (no-crime cases), such as when a fire with natural or accidental origins leads to an erroneous conviction for arson. Causes of wrongful convictions may include eyewitness misidentification, unvalidated or improper forensic science, false confessions, inadequate assistance of counsel, coerced pleas, and official misconduct. A wrongful conviction based on possible factual innocence can sometimes be detected using postconviction DNA testing.[1]

Although we know that some share of innocent people are convicted of crimes, we do not know exactly how often that happens. Research findings funded by NIJ estimate the prevalence of wrongful conviction at less than 5% of all convictions.[2] The latest rigorous NIJ-funded estimate supports this rate; however, variations in the rate of error by crime type and other factors may exist.[3] Wrongful conviction research has also observed that exonerations likely represent just a small fraction of the true number of erroneous convictions that have occurred.

This uncertainty largely stems from issues with the data.[4] Wrongful conviction rates are estimated based on known convictions. Given the amount of time and resources needed to discover and work towards an exoneration, efforts of innocence projects and conviction integrity units tend to be focused on major crimes. For lesser crimes, and especially those for which the conviction is the result of a plea deal, the resources needed to produce an exoneration may not seem justified.

Much of what we know about wrongful convictions in the United States comes from databases of cases made available by the Innocence Project[5] and the National Registry of Exonerations. Each organization provides information about individuals who were convicted of crimes and later formally exonerated, meaning their convictions were invalidated and official action indicated their innocence (for example, the charges were dismissed, they were acquitted on retrial, or they received an executive pardon). As of March 2024, The National Registry of Exonerations has identified over 3,400 exonerations in the United States.[6]

Every wrongful conviction is a miscarriage of justice that affects all levels of our society. Their outcomes have life-long impacts on the people who have been wrongfully convicted, the original victims of crime, and the families of both parties. Wrongful convictions undermine the confidence our nation has in the criminal justice system, often leading to questions about its fairness, especially since these errors disproportionately affect people of color.[7] In addition, wrongful convictions result in “wrongful liberty,” where the individuals who truly committed the crimes are free to victimize others.  

As the research, development, and evaluation agency of the U.S. Department of Justice, NIJ is dedicated to using science to learn more about wrongful convictions. Understanding the causes and consequences can help us identify ways to prevent these types of errors in the future and to address the needs of those who have been affected by erroneous convictions. Doing so is an important step in ensuring public confidence in the justice system.

Reading and Resources


[note 1] See National Institute of Justice funding award description, “Postconviction DNA Program,” at Cook County State’s Attorney’s Office, award number 2015-DY-BX-K007, https://nij.ojp.gov/funding/awards/2015-dy-bx-k007; National Institute of Justice funding award description, “2015 Postconviction DNA Testing Program,” at North Carolina Administrative Office of the Courts, award number 2015-DY-BX-K001, https://nij.ojp.gov/funding/awards/2015-dy-bx-k001; and other awards made under National Institute of Justice funding opportunity, “NIJ FY 15 Postconviction Testing of DNA Evidence to Exonerate the Innocent,” grants.gov announcement

[note 2] John Roman et al., “Post Post-Conviction DNA Testing and Wrongful Conviction,” Final report to the National Institute of Justice, award number 2008F-08165, June 2012, NCJ 238816, https://www.ojp.gov/pdffiles1/nij/grants/238816.pdf.

[note 3] John Roman et al., “Post-Conviction DNA Testing and Wrongful Conviction.” See also, Kelly Walsh et al., “Estimating the Prevalence of Wrongful Conviction,” Final Report to the National Institute of Justice, award number 2013-IJ-CX-0004, September 2017, NCJ 251115, https://nij.ojp.gov/library/publications/estimating-prevalence-wrongful-convictions. This study found a much higher rate when just looking at sexual assault cases with a determinate DNA sample.

[note 4] See Gross, S. et al., “Rate of False Conviction of Criminal Defendants Who are Sentenced to Death,” Proceedings National Academy of Sciences 111 (2014): 7230-5.

[note 5] See https://innocenceproject.org/

[note 6] See https://www.law.umich.edu/special/exoneration/Pages/about.aspx.

[note 7] See “Race and Wrongful Conviction,” Innocence Project, https://innocenceproject.org/race-and-wrongful-conviction/#:~:text=Indeed%2C%20a%202022%20report%20from,in%20the%20criminal%20legal%20system.

The use of drones, or unmanned aircraft systems, to deposit contraband, such as drugs, weapons, and cellphones, into correctional facilities poses a significant and growing threat to the safety and security of prisons and jails. Advances in drone technology have enabled remotely piloted aircraft to carry larger payloads, fly faster and longer distances, and operate at lower costs. Most drones suited to prison incursions are fast, quiet, and small enough to be difficult to detect with the human eye.

More research is needed to both quantify the drone-delivered contraband threat in correctional facilities and identify all its dimensions. Technology that can detect and defend against drones is also advancing in efforts to meet this emerging threat.  

These efforts are complicated by the need for regulators and correctional leaders to ensure that new strategies to capture or intercept signals from drones do not violate federal communications laws.  

NIJ’s Criminal Justice Testing and Evaluation Consortium has generated research and reports on several aspects of contraband management and defenses, including the report, “Contraband and Drones in Correctional Facilities.” 

Reading and Resources 

Additional CJTEC reports on contraband

In criminology, push and pull factors are conditions that lead to or attract people away from criminal behaviors or extremist ideologies.  

Push factors generally comprise negative or adverse conditions that make crime or extremism seem like a good option. For example, social isolation might "push” an individual to join a gang. Pull factors entice individuals toward crime or extremism for the perceived benefits. For example, the desire to reinforce a social or religious identity might “pull” an individual toward a radical ideology aligned with that identity.

Push and pull factors can also shape a person’s trajectory away from crime or extremism. Someone disengaging from a terrorist group might be pushed away from extremism when they become disillusioned with the group’s tactics. Or they might pull away from extremism when they become a parent and want to provide a stable life for their child.  

Issue 285 of the NIJ Journal focuses on domestic radicalization, violent extremism, and terrorism. Much of this research describes how individuals are pushed toward or pulled away from extremism based on various factors. It’s important to note that every person is different. How individuals respond to push and pull factors depends on their backgrounds and experiences; factors that cause a behavior change in one person may have no effect on another. 

Reading and Resources 

The term “cold case” is typically used by law enforcement to describe a criminal case, often a homicide or sexual assault, that has remained unsolved for an extended period with no fresh investigative leads to be pursued. The length of time before a case is officially classified as a cold case differs from jurisdiction to jurisdiction, and timeframe can depend on the seriousness of the crime. Arizona, for example, defines a cold case as any crime that remains unsolved after a year, while Los Angeles classifies homicides that have gone unsolved for five years or more as cold.

The share of homicides that are designated as cold cases is likely increasing, based on the decline in homicide clearance rates over time, which the FBI’s Uniform Crime Reports indicate dipped from 80% in 1965 to about 61% in 2019. With fewer cases solved in any given year, it stands to reason that more remain cleared over time. In fact, an analysis of clearance rates from 1980–2017 led experts to estimate that approximately 250,000 unresolved homicides exist in the United States, and more than 100,000 have accumulated since the late 1990s.

These numbers are likely fueled by the fact that establishing cold case investigative units is expensive, and law enforcement agencies often lack the personnel to work the cases. The cases are cold because they proved difficult to solve to begin with, and as time passes the reliability of both witnesses and stored evidence can fade.

However, scientific techniques are rapidly improving, allowing for more precise DNA analysis, familial DNA searches, and more sophisticated computer systems to examine forensic evidence. New, cooperative cold case investigative units bring together expertise from different agencies and are successfully illuminating old cases. NIJ has long history of supporting cold case reviews, including support of the National Missing and Unidentified Persons System (NamUs). In 2019 NIJ initiated the “Prosecuting Cold Cases using DNA and Other Forensic Technologies” program to help with the resolution of the growing number of cases. In 2020, this program moved to the Bureau of Justice Assistance, which has continued its support.

Reading and Resources 

Implementation science helps us learn how to bring effective solutions into real-world settings. When research studies reveal what works and what doesn’t, implementation science helps us understand what it takes to ensure that proven strategies are adopted, properly implemented, and sustained in various contexts. This field of study aims to bridge the gap between science and routine practice. Implementation science guides one of NIJ Director Nancy La Vigne’s priorities: “ensuring that research evidence is translated into actionable information to promote change in the field.”

In fiscal year 2024 NIJ anticipates releasing a solicitation on “Evaluating Strategies to Advance the Implementation of Evidence-Based Policies and Practices.” With it, NIJ will seek proposals for rigorous demonstration of and research projects to further the use and impact of existing crime and justice research evidence. Specifically, NIJ will seek to fund research that leverages implementation science knowledge and promotes evidence-based policy and practice — most directly by developing, supporting, and evaluating efforts to improve research evidence use by policymakers, agency leaders, intermediaries, and other decision-makers who shape justice outcomes.

Reading and Resources 

Torso-worn body armor, commonly referred to as vests, helps protect law enforcement officers from weapons such as guns and knives. Through body armor standards and the Compliance Testing Program, the National Institute of Justice (NIJ) provides law enforcement and corrections agencies and individuals with information about commercial body armor performance. NIJ’s body armor standards provide minimum performance requirements for both ballistic and stab resistant vests, while the Compliance Testing Program allows manufacturers to submit their body armor products for testing to see if they meet the national standard.  

NIJ will be publishing a revision to the performance standards for ballistic resistant body armor later this month, with updates including improved test methods for armor designed for women, additional test requirements for both soft and hard body armor, and several standardized procedures and test methods published by ASTM. Ballistic threat tests were part of the previous body armor standard but now will exist as their own standard: “Specification for NIJ Ballistic Protection Levels and Associated Test Threats.” This specification describes which bullets and velocities should be used to test ballistic resistant equipment in conjunction with other performance standards.

Ballistic Resistant Armor

Stab Resistant Armor

See a full list of all NIJ’s active standards

Trace DNA, also known as “low copy number DNA” or “touch DNA,” refers to small amounts of DNA left on objects. Trace DNA may originate from shed skin cells from the outer layer of an individual’s hand, or from cells of other body parts or fluids on the hand (e.g., saliva, eyes, nasal fluids). As DNA detection techniques have continued to improve, scientists have become aware of the ability of DNA to be transferred between objects. For example, crime scene investigators who use fingerprint brushes may unknowingly transfer trace amounts of DNA from one surface to another, which may generate misleading results. Because trace DNA deposited on a surface is not visible to the naked eye, it can be difficult to predict the presence or quantity of DNA with the same confidence as one might link a DNA sample isolated from a visible blood stain. For this reason, many forensic investigators prefer to decouple the analysis of trace DNA from specific activities or locations.  

In 2018 and 2023, the NIJ Forensic Science Research and Development Technology Working Group called for comprehensive, systematic, well controlled studies that provide both foundational knowledge and practical data about DNA transfer and persistence (the duration of time that the DNA deposit remains detectable). Understanding the behavior of trace DNA deposits should inform how scientists recover, analyze, and interpret this type of evidence. NIJ has supported multiple projects focused on trace DNA analysis. 

Reading and Resources 

Conjunctive analysis of case configurations is an exploratory data analysis technique that looks at how multiple variables interact. 

Many data analysis techniques examine one factor at a time while controlling for all other factors. Conjunctive analysis, on the other hand, examines many risk factors simultaneously. It looks at the complex causal relationships between these factors and how they interact to determine different outcomes.  

Terance Miethe, Timothy Hart, and Wendy Regoeczi developed and introduced conjunctive analysis to the criminology field in 2008. Since then, researchers have used the statistical method to better understand patterns in carjacking incidents, intimate partner violence, crime and the distribution of alcohol outlets, police discretion, and the violent victimization of university students. Researchers have also used conjunctive analysis to study homicide investigations, child sexual abuse, robbery risk factors, missing person case outcomes, sentencing disparities, terrorism risk profiles, and more. 

Reading and Resources from NIJ: 

Other Resources: 

Metabolites are substances made when the body breaks down food, drugs, or even its own tissue, such as fat or muscle in the body, while also ridding the body of toxic substances. This process, known as metabolism, creates the energy and makes the materials needed for growth, reproduction, and health maintenance.  

Metabolites excreted by the body, usually in urine, can help investigators discern if a person ingested a specific drug. Metabolites are known as markers for one or more parent drug, and the amount and types of metabolites present in a sample can indicate what drug a person has consumed. 

For example, heroin quickly metabolizes into a chemical called 6-acetylmorphine (6-MAM), which the body converts, typically within a half hour, into morphine. A similar process occurs with fentanyl, which metabolizes into norfentanyl. 

Research is ongoing to determine if metabolites can serve as a postmortem indicator of a person’s time since death, but these studies are in the exploratory stages. Other research is exploring the utility of postmortem metabolic profiling in determining whether cardiovascular diseases, cancers, or diabetes contributed to a death. 

Reading and Resources:

Drug treatment courts are specialized court docket programs that target persons who have alcohol and other drug dependency problems within the criminal justice system, including adults charged with or convicted of a crime, youth involved in the juvenile justice system, and parents with pending child welfare cases. Although drug courts vary in target populations and resources, the programs are generally managed by a multidisciplinary team that includes judges, prosecutors, defense attorneys, community corrections officers, social workers, and treatment service professionals. Support from stakeholders — representing law enforcement, family, and community members — can participate in hearings, programming, and events, such as graduation. Various types of drug courts have emerged to address issues relevant to specific populations, including tribal healing to wellness, driving while intoxicated, reentry, veterans, mental health, and co-occurring programs. 

Reading and Resources:

The field of forensic toxicology combines the principles of analytical and clinical chemistry with pharmacology to aid in medicolegal investigations of drug use, poisoning, and death. Forensic toxicologists determine which non-endogenous (non-naturally occurring) toxic or intoxicating substances are present, in what concentrations, and the probable effect of those chemicals on the individual.

Forensic toxicology includes human performance toxicology (antemortem) and postmortem toxicology. Forensic toxicologists analyze fluid samples, which include blood, urine, and oral fluid, as well as tissue samples such as hair, nails, and organ tissues.

Reading and Resources:

The forensic intelligence model is an analytical strategy that combines using forensic data (both preliminary and confirmed results) with situational and other relevant crime data (such as open-source databases) to produce case leads, link cases, or inform investigative, tactical, operational, or strategic policing. In this strategy, data derived from the forensic analysis of physical evidence can inform the investigation. The forensic data produced for forensic intelligence may not necessarily be the complete forensic report needed for presentation in court, but it can potentially inform investigations if integrated in a timely manner. 

Law enforcement can use this model to identify crime trends, guide investigations, and enhance public safety. It allows investigators to leverage local forensic testing results and supporting details from local, state, and even federal law enforcement databases, to create a package that is generally easier to digest than a traditional forensic laboratory analysis. 

Collectively, forensic intelligence is based on the subject matter experts’ cumulative experiences from the field, the published literature on the topic, and discussions with other experts. Before using this approach, law enforcement should consider their organizational structure, key partnerships, communications capabilities, and the development of necessary resources. The goal is to eliminate silos of information and encourage communication regarding the connectivity of all the evidence for a specific case, linking cases and informing policing strategies to prevent crime. 

Reading and Resources:

Reentry involves an individual’s transition from life in jail or prison to life in the community. Similar to desistance, reentry is a process or continuum of change where consistent support is crucial for the transitioning individual. 

Support can take many forms. Research shows that housing, employment, family unification, mental and physical health treatment, and meeting other critical criminogenic needs are vital to fostering post-release success. However, the reentry process looks different from person to person, and programs and services should be tailored to meet an individual’s unique needs. 

NIJ continues to support research to improve our understanding of how to better support an individual when they reenter and to inform criminal justice policy and practice. Specific research investments include assessing the impact of young adult reentry programs and examining the effects of traumatic brain injury on criminal justice outcomes such as recidivism and employment. Examinations of risk-need-responsivity strategies and innovative treatment modalities also require research investment, as emerging technologies, including the development of AI and machine-learning tools, have the potential to increase our understanding of reentry and recidivism. NIJ will continue its three-decade long investment in reentry research to help the field answer important questions, with a renewed focus on rigorous research designs. 

Reading and Resources:

Polyvictimization can generally be defined as the experiences of multiple, distinct types of violence, abuse, mistreatment, and other adversities. Although polyvictimization has been defined and operationalized in different ways across the literature, it typically refers to two or more different types of victimization — such as sexual violence, physical abuse, or exposure to family and community violence — rather than multiple episodes of a single type of victimization.

The polyvictimization framework has recently been used to study the abuse of older adults. According to one NIJ-funded study with a nationally representative sample of community-residing older adults in the United States, approximately 2% of older adults experienced polyvictimization in the past year. This translates to over 970,000 older adults. Risk for polyvictimization was greater among older adults who experienced problems accomplishing activities of daily living (for example, shopping for groceries or medicines, bathing), those with low social support, and those who had experienced a past traumatic event. Another NIJ-funded study found that multiple types of polyvictimization in older adults are related to poor physical and mental health outcomes and mortality.

Polyvictimization among children and youth has also been examined and can occur in a variety of settings, including families, schools, communities, and online. Children may be repeatedly traumatized as they are victims and witnesses of multiple abusive experiences, including child abuse, neglect, domestic violence, sexual exploitation, school violence, trafficking, gun violence, hate crimes, dating violence, or bullying.

Select Resources:

A replication study is a scientific study that attempts to validate findings from prior research by asking the same or similar scientific questions as the original research study. Replication matters because the peer review process alone does not guarantee the integrity of the reported results. Replication studies strengthen science by independently confirming the validity of research findings. When results are consistent across studies, the results of the original study are more likely to reliable.  

Research is generalizable if a second study addresses a similar scientific question and finds consistent results in contexts or populations that differ from the original context or populations.

Not all scientific studies can be replicated. Non-replicability can be the result of uncertainty, or study limitations, such as:

  • Publication bias
  • Misaligned incentives
  • Inappropriate statistical inference
  • Poor study design
  • Researcher errors
  • Incomplete reporting of a study

In the social sciences, economics, clinical studies, and other fields, replication studies often include new data collections to verify original findings. A different term, reproducibility, measures whether a second study using the same data and the same or similar procedures as the original research yields consistent results.

The National Institute of Justice requires all research grantees to deposit data collected during the life of an award with the National Archive of Criminal Justice Data, an archive of datasets maintained for secondary analysis, to allow for replication studies.

NIJ research grant solicitations regularly encourage grant proposals for replication research.

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Risk terrain modeling is a science-based method of identifying and measuring crime risk posed by the features of a specific physical location — for example, a parking lot, a convenience store, a bar, or a vacant building.

Risk terrain modeling is a tool designed to diagnose crime location patterns. Risk terrain modeling software generates an overall crime risk value for specific locations and explains which terrain features contribute to crime risk.

Assigning a risk value to each characteristic of a location allows public agencies to isolate those characteristics, or combinations of characteristics, that most influence crime.

Two important advantages of risk terrain modeling, in comparison to other proactive policing methods, are:

- Scope of resource response to locations at risk: By identifying the characteristics of a place associated with increased risk of crime, risk terrain modeling creates opportunities for comprehensive responses not limited to law enforcement action. For example, if poor lighting is found to elevate crime risk, then the streets department could be asked to improve it.

- Fourth Amendment protection from unreasonable search and seizure: Risk terrain modeling focuses on attributes of a place, not of a person. Thus, the use of risk terrain modeling to guide officer actions generally may be less likely than other proactive policing methods to be associated with a risk of constitutional rights violations.

By pinpointing crime risk associated with specific places on a map, risk terrain modeling can help guide geographic distribution of law enforcement and other public resources.

Research on the application of risk terrain modeling in multiple communities has found it to be an effective and accurate method of identifying crime risk and altering the characteristics of a place to prevent crime problems.

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Expungement is the process by which a record of criminal conviction is destroyed or sealed from state or federal record. An expungement treats the conviction as if it had never happened, removing it from an individual’s criminal record and, ideally, the public record. However, in the digital age, completely removing any information in the public record has become challenging.

Most expungement proceedings take place in state courts. Each state has its own distinct laws about who is eligible for expungement, which offenses can be expunged, and how records will be managed. Some states have “clean slate” laws that require the state government to automatically expunge minor criminal records for qualifying individuals. Other states require individuals to petition the court to clear part or all of a criminal record.

An individual’s criminal record can create significant reentry barriers. For example, a record can thwart efforts to secure housing or gain employment. Expunging an individual’s criminal record, where appropriate, can be critical to their ability to move forward and live a law-abiding life.

It is important to note that an expungement is not the same as “forgiveness” for committing a crime — that is known as a legal pardon. 

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A black box study design can be used to measure the overall behavior of a complex system. It disregards the internal processes and simply measures how the final output changes depending on the input. Black box testing has long been used to study complex systems in software engineering, physics, and psychology.

In the forensic sciences, researchers use black box studies to measure the accuracy and reliability of forensic disciplines as they are currently practiced. This includes latent fingerprint examination, bloodstain pattern analysis, forensic firearms examination, and others. These disciplines largely depend on subjective comparison of evidence by human experts. The researcher uses a set of samples with known “ground truth” and treats the examiner as a black box, measuring how often their conclusions are right or wrong. This is important information for the courts to consider when deciding whether to admit forensic testimony.

Conversely, a “white box” study — in the context of forensic science — looks at the details of the examiner’s thought process or methodology to determine which factors have the most effect on the outcome. It allows the researcher to look inside the black box and gain insight into how and why examiners reach their conclusions.

Select Resources:

Read an NIJ Journal article on the history and legacy of an influential black box study examining the accuracy and reliability of latent fingerprint examination. Results from a black-box study for digital examiners by the National Institute of Standards and Technology.

Subadult is a categorization used by anthropologists, including forensic anthropologists, to define human skeletal remains believed to be from a person whose age-at-death was 20 or younger. Investigators traditionally have used pelvic differences between males and females and the predictable development of teeth to try to determine the sex and age of skeletal remains of infants, children, and adolescents, but that information is often insufficient to make an accurate determination.

Investigators also look at long bone lengths (femur and tibia, for example) and the fusion growth plates in bones (epiphyseal fusion) to determine age-at-death, but those indicators are only useful during specific periods of a person’s growth and, without a large database for comparison, individual measurements are limited in what they can reveal.

New research is expanding the markers scientists can use to include spinal canal measurements, cranial shape and form measurements, and detailed measurements of the shape and form of teeth. This research, when combined with growing databases of subadult skeletons, is allowing investigators to consider a wide range of markers for determining age and sex, as well as population affinity (ethnicity).

Increasing the number of markers is important because they change significantly as a subadult grows from infancy through adolescence, and the presence or absence of a marker can narrow the age range.

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Virtual comparison microscopy is the use of high-resolution 3D surface scanning and measurement in the field of firearm and tool mark analysis. The accurate surface imaging of bullets and shell casings with 3D visualization tools and advanced algorithms allow forensic examiners to view, annotate, conduct blind verification, and develop a statistical basis for identifying and matching ballistics evidence.

With a virtual comparison microscopy system, the bullets and casings are scanned, creating a detailed topographical map that can be shared between crime labs. The electronic file allows for the verification of findings by a second examiner. The traditional 2D comparison method requires the actual evidence — spent bullets or shell casings — to be examined directly.

Because virtual comparison microscopy files can be easily shared, they allow for better training, error-rate studies, and proficiency testing in crime labs. Although researchers expect human examiners to conduct ballistics testing for the foreseeable future, as the database of bullets, casings, and guns grows, sophisticated algorithms and machine learning could allow computers to play a significant role.

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A student threat assessment is a systematic approach to evaluating the likelihood that a student will carry out a violent act after an expressed threat or threatening behaviors.  

Threat assessments are performed by interdisciplinary school-based teams. The teams can give schools a proactive, effective alternative to reactive disciplinary practices such as zero tolerance discipline and exclusionary discipline such as student suspensions.  

Threat assessments can prove challenging, however. Schools must substantiate information received in threat assessments, and threat assessments will not be a practical means of assessing all tips related to threatened school violence. 

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Deradicalization refers to an individual’s or group’s disavowal of, or shift away from, extremist beliefs that can support terrorism. The term can also refer to policies, practices, or strategies designed to advance a deradicalization process. Deradicalization is one element of a comprehensive approach to preventing extremist violence.  

NIJ continues to support research on deradicalization and related topics. A 2022 NIJ research solicitation called for “research to better understand the deradicalization and disengagement phenomena. NIJ is particularly interested in understanding factors that promote withdrawal and independence from extremist behaviors, as well as those factors that play a role in encouraging individuals to depart radical ideologies (or at least shift away to less-extreme beliefs).” 

Microbial forensics is the investigation of the cloud of biological evidence humans leave behind at crime scenes that includes bacteria, fungi, viruses, and other microbial evidence. Researchers have learned over the past 20 years that each person carries a distinct microbial signature that is shed into the environment and left on objects that are touched. The number of microbes in the biological clouds that surround each of us is enormous, but because they are invisible to the eye, we are unaware of them.   

The microbial communities living in association with the human body make up an individual’s microbiome, and the bacteria alone are typically 10 times more prevalent on a body than human cells. About 3% of a person’s body mass is made up of microbes. 

The birth of microbial forensics came with the 2001 attacks in Washington, D.C. using anthrax spores. The efforts to identify the strain of anthrax established microbial forensics as an investigative tool, and since that time it has been used to detect microbial traces on phones, doorknobs, keyboards, and other objects a suspect may have touched. In the future a microbial signature may reveal details about a person’s diet, health, and drug use. 

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Unmanned aircraft systems is a term that encompasses not only the unmanned aircraft vehicle but also the flight controller on the ground, and the system of communication between the two. Under FAA Part 107, unmanned aircraft vehicles are air vehicles weighing between a half and 55 pounds that operate by remote pilot and are often fitted with specialized cameras, GPS, and/or other sensors that collect and often relay information via a communications link to a variety of destinations, including the remote pilot and/or a command center. In law enforcement, unmanned aircraft systems are used in a variety of ways, including crowd control, traffic and accident reporting, search and rescue, crime scene reconstruction, pre-operational situational awareness to optimize officer and individual safety (e.g. by gathering information for bomb threats and hostage situations), and even as first responders. 

Unmanned aircraft systems are subject to the rules set forth by the Federal Aviation Administration to maintain safe national airspace, specifically Unmanned Aircraft Rules (Part 107). Since unmanned aircraft systems also are operated from a remote command and control center and relay information, equipment must be certified by the Federal Communications Commission to minimize harmful radio interference. Most unmanned aircraft system pilots are required to maintain visual-line-of-sight (VLOS) with their aircrafts, with the exception of those who have beyond-visual-line-of-sight (BVLOS) certification. 

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Community corrections is a term for managing individuals convicted of a crime and serving their sentences in a community setting, rather than in prison or jail. Community supervision is another term for community corrections. Probation and parole are two primary forms of community corrections. Community supervision may also be ordered for individuals awaiting trial.  

Probation is an alternative to jail, or sometimes prison, ordered when the sentencing court decides that the crime does not warrant incarceration. Probation officers supervise individuals on probation, monitoring their activities and ensuring compliance with conditions of supervision. Conditions of supervision include avoidance of crime and association with individuals with felony sentences and may include school attendance, employment, testing for drugs or alcohol, or other milestones to be met by the sentenced individual. 

Parole is supervised release from prison after a portion of a sentence has been served. Parole is granted when a parole board or other authorized public body determines that release of an individual from confinement is justified in light of evidence of rehabilitation and public safety interests. Persons on parole, like those on probation, regularly meet with supervision officers and satisfy conditions of parole to complete their sentence.  

The philosophy underlying community corrections is to prevent criminal behavior through close supervision and the imposition of restrictions on probation or parole in an environment designed to be more conducive to rehabilitation while maintaining public safety. A related goal of community corrections is the reduction of overcrowding of prisons and jails. 


Situational crime prevention (SCP) is a crime reduction strategy used by law enforcement that stemmed from the analysis of circumstances that give rise to particular types of crime. SCP posits that criminal acts may be deterred by strategic environmental or managerial changes. It differs from other crime prevention strategies because it focuses on the setting for crime, rather than those committing criminal acts. The main goal of situational crime prevention is to make criminal acts less attractive to people who might potentially offend.  

There are a multitude of ways this can be accomplished, including increasing the risk and reducing the reward of committing a crime, removing the target, increasing surveillance, controlling weapons, and alerting the offending person’s conscience. As such, it requires assistance from the leadership at a number of public and private locations that tend to attract crime, including schools, hospitals, parks, bars, stores, and transit. 

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Related articles: 

There also are promising practices related to situational crime prevention on CrimeSolutions: 

NIJ continues to fund research with the goals of understanding the effects and usefulness of situational crime prevention. Ongoing research projects include:  

A major theory in socio-behavioral and other sciences, life course theory posits that individual life experience is connected to dynamics that are driven by historical and socioeconomical factors.  

In the criminological context, the central idea of life course theory is that childhood antisocial behavior, adolescent delinquency, and early adult criminal infractions are more likely when an individual's bond to society is weak or broken.[1] It stresses turning points that may occur over an individual’s life course which affect their connection to society and its institutions, levels of social control, and thus likelihood to become involved in criminal behavior.  

The theory is an effort to offer a comprehensive outlook on the study of criminal activity by considering a multitude of factors that affect offending across different time periods and contexts. The goal is to explain the onset of, persistence of, and desistance from offending behavior over the life course of an individual.  

Read more about life course theory and desistance from crime.

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[note 1] Sampson, R.J. & J.H. Laub. (1993). Crime in the Making: Pathways and Turning Points Through Life. Boston: Harvard University Press.

The Trafficking Victims Protection Act (TVPA) of 2000 was the first Federal law to address the trafficking of persons, aimed at the prevention, protection, and prosecution of both labor trafficking and sex trafficking. The TVPA created the most widely accepted definition of labor trafficking: "the recruitment, harboring, transportation, provision, or obtaining of a person for labor or services, through the use of force, fraud, or coercion for the purpose of subjection to involuntary servitude, peonage, debt bondage, or slavery” (DHS Human Trafficking Laws & Regulations).

Per the National Action Plan to Combat Human Trafficking, “Labor trafficking occurs across many different industries, including domestic work, traveling sales crews, food services, peddling and begging, agriculture, health and beauty services, construction, hospitality, and landscaping.”

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NIJ continues to fund research with the goals of understanding and preventing labor trafficking. Select ongoing research projects:

Machine learning is the study of computer algorithms that improve automatically through experience. It refers to the development of systems that can learn from data. A machine learning algorithm can, after exposure to an initial set of data, evaluate new, previously unseen examples and relate them to the initial “training” data. It is ideally suited for classification problems that involve implicit patterns, and it is most effective when used in conjunction with large amounts of data. 

Criminal justice applications of machine learning include detecting patterns and anomalous behavior, predicting crowd behavior and crime patterns, protecting critical infrastructure, and uncovering criminal networks.

Read an NIJ Journal article on the role of machine learning in criminal justice.

Desistance is generally understood to mean the reduction in criminal behavior over time. It is the process of individuals ceasing engagement in criminal activities. Varying definitions and measurement strategies have evolved over the years. Early scholarship tended to view desistance as a discrete event — that is, the termination of offending or end of a criminal career. More recent definitions, however, suggest that desistance is instead a developmental process by which criminality declines over time.

In NIJ’s new publication Desistance From Crime: Implications for Research, Policy, and Practice, Dr. Michael Rocque offers an updated, theoretically grounded definition as a foundation for future work: Desistance is “the process by which criminality, or the individual risk for antisocial conduct, declines over the life-course, generally after adolescence.”

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Historically called domestic violence, intimate partner violence describes physical, sexual, or psychological harm by a current or former intimate partner or spouse. Types of intimate partner violence include physical violence, sexual violence, threats of physical or sexual violence, psychological/emotional violence, and stalking. 

Violence by an intimate partner is linked to both immediate and long-term health, social, and economic consequences. Factors at all levels — individual, relationship, community, and societal — contribute to intimate partner violence. This type of violence can occur among heterosexual or same-sex couples. 

Preventing intimate partner violence requires reaching a clear understanding of those factors, coordinating resources, and fostering and initiating change in individuals, families, and society. 

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Dual system youth are a subset of “crossover youth” — juveniles who have been victims of maltreatment and have also engaged in delinquent acts. The dual system youth population consists of crossover youth who have entered, at some point, both the child welfare and juvenile justice systems. This vulnerable and high-risk group has unique, complex needs that demand a collaborative approach by the child welfare and juvenile justice systems. 

The Dual System Youth Design Study, led by investigators at California State University Los Angeles and supported by NIJ and the Office of Juvenile Justice and Delinquency Prevention, suggests that more than half of the juvenile justice population has or will have child welfare involvement. 

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In forensic science, an alternate light source uses monochromatic light to detect and identify physical evidence, including bruises, body fluids, hair, clothing fibers, and other trace materials. This technology takes advantage of a material’s inherent luminescent properties that cause it to glow when struck with a specific wavelength of light.  

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Novel psychoactive substances (NPS), also referred to as designer drugs and synthetic drugs, are an emerging or re-emerging type of illicit substance. NPS are similar in structure and effect to common drugs of abuse, but differ enough that they evade detection with traditional tests and require new scheduling laws. NPS pose serious complications for both consumers and forensic scientists because their use may be linked to severe health problems and their chemical modifications makes them difficult to identify.

Read about research on NPS in the NIJ Journal article, Identifying New Illicit Drugs and Sounding the Alarm in Real Time, and in an article written by NIJ scientist Frances Scott, NPS Discovery and the Hunt for New Drugs of Abuse

Mass spectrometry is a tool for measuring different fragments of a compound. In forensic science, mass spectrometry can be used, for example, to identify and discriminate individual drugs in seized substances. A mass spectrometer takes a sample, ionizes and breaks the compounds in it, and sorts the fragments by the ratio of their weight to their charge. The pattern of the captured fragments makes a spectral signature that can be used to identify the compound.

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NamUs is a national repository and resource center of information related to missing, unidentified, and unclaimed person cases. Funded and administered by the National Institute of Justice, NamUs fills the nation’s need for a central, online, secure database of unidentified remains and missing persons records. The database is searchable by all, with biometric and other secure case information accessible only to appropriate, vetted criminal justice users. All NamUs resources are provided at no cost to law enforcement, medical examiners, coroners, allied forensic professionals, and family members of the missing.

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Reintegration is when an individual transitions from being incarcerated in a prison or jail to living in a community and attempting to maintain a crime-free lifestyle.

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Technology-facilitated abuse refers to harmful acts or courses of conduct facilitated through digital means that can compromise victims’ privacy and cause them to fear for their safety. Examples of such conduct are cyberstalking, nonconsensual pornography, swatting, doxing, and sextortion.

Personal harm from digital abuse extends far beyond the digital realm. These acts can cause serious psychological distress and damage relationships with family, friends, and partners and disrupt educational and professional pursuits.

Sextortion — A form of cyber extortion featuring an online attack on victim systems, for example through ransomware, in which and individual demands sexual images, sexual favors, or other things of value in exchange for stopping the attack.

Nonconsensual pornography — Distribution of nude or sexually explicit images or videos of an individual without consent.

Cyberstalking — Repeated use of electronic communications to stalk a person or group.

Doxing — Public release of private and sensitive personal identifying information about an individual without their consent. (The word “doxing” is derived from “documents.”)

Swatting — False report of an emergency to trigger an emergency response, specifically deployment of a SWAT team, to a location where no emergency exists.

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Pediatric bruising patterns are tell-tale bruising patterns in injured children in order to differentiate between accidental injuries and physical abuse. Bruising on a child’s ear, buttocks, feet, or hands, for example, are not typical of accidental injuries and should alert physicians to possible abuse. 

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Using data, analysis, and research to complement experience and professional judgment, in order to provide the best possible police service to the public.

Evidence-Based Policing refers to scientific evidence, not evidence in the legal or investigative sense.

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Research for the Real World - Evidence-Based Policing: The Importance of Research and Evidence, July 2018
Date Created: January 28, 2021