U.S. flag

An official website of the United States government, Department of Justice.

Caution Is Necessary When Expanding Field Testing Capabilities

Notes From the Field
Date Published
January 5, 2021

Forensic laboratories operate in a world with two constant, competing pressures — law enforcement’s needs and demands for quick results, and the scientific responsibility to ensure those results are accurate.

The push for ever faster results is immense and understandable. Laboratories are backlogged, driving investigators to try to find a path to necessary results.

Field testing evidence before it is submitted to a lab is one avenue toward more immediate results, but it should come with caution signs.

The closer forensic testing gets to the field and the farther away from the more controlled environment of a lab, the greater the risks that tests may not be performed correctly or the results may be misinterpreted. When forensic testing is removed from the lab and placed in the field, it opens up many possibilities for evidence to be destroyed or contaminated and for results to be used in ways that exceed their appropriate scope.

As you strip away the safeguards that laboratory processes are specifically designed to ensure, a hazardous slide toward false positive results becomes more and more likely.

Field Testing Gone Sideways

Here in Houston, hundreds of wrongful convictions overturned in recent years were caused by inexpensive field tests for drugs that have been shown to produce a high rate of false positives. In the end, laboratory tests eventually brought the correct results and led to many exonerations in these cases.

Those field tests are no longer used in Houston, and the District Attorney’s Office implemented a new policy that any positive field test needs to be confirmed by the laboratory before the defendant can enter a guilty plea.

This is illustrative of how incredibly difficult it is to engineer and reliably implement technologies the closer you get to the field. Think of why laboratories exist: They are an effort to control conditions, organize materials, and reduce distractions.

Now, imagine a police officer performing tests on an unknown substance on the hood of a patrol car. It’s nighttime and there are red and blue lights flashing all around. Meanwhile, to interpret the results of the test, the officer needs to determine if the substance dropped into a small bag of chemicals produces a color change to red, purple, or blue, indicating illegal drugs. It's easy to see how the results of this test could be misinterpreted under those difficult circumstances.

Former Houston Police Chief Charles McClelland summarized it best when he said officers shouldn’t be conducting experiments on the hoods of their patrol cars. He was right — these tests don’t typically end well for anyone, and the challenges they create extend far beyond the officer in the field.

Consistent and reliable documentation, data storage, and reporting language are critical in forensic testing. The lack of these established processes can lead to further misunderstanding or misinterpretation of results and an inability to access underlying data for the courts to fairly adjudicate a case.

Rapid DNA Testing Pilot Program

Another example of a new technology that has caused problems in Houston is Rapid DNA.

Rapid DNA instruments use the same chemistry as laboratory tests, but the danger comes with using the machine ever closer in both time and space to an emotionally raw and chaotic crime scene. Those circumstances increase the possibility of evidence contamination, as well as the potential for results to be misused.

Since Rapid DNA tests destroy the sample, two samples need to be taken at a scene. If that second DNA swab isn’t recorded and preserved following a test, there’s no way for a laboratory to confirm the initial result or retest the sample years later when a new, more advanced technology is available.

In 2017, we experienced some of these issues while we were involved with a pilot program that included the Houston Police Department and a Rapid DNA manufacturer.

Our problems arose not from the equipment or the results it produced — these are highly automated devices that produce accurate results. Rather, it was the situation surrounding the use of the instruments that created problems. We had instances where our agreed-on protocol — that the first swab would go to the lab and a second swab would be used for the pilot program — was inconsistently followed.

This led to compromised cases in which evidence was destroyed either in the process of swabbing or after it was analyzed. We also had cases where evidence was swabbed and analyzed but never disclosed to the laboratory, compromising the future prosecution of the case.

Overall, it was not a productive pilot program, though it did expose where some dangers lie.

Trouble Accessing Phone Data

Another common way field testing can go awry is with smartphone data. In the early stages of an investigation, investigators are often interested in the text messages, contacts, and email addresses associated with a mobile device found at a crime scene.

This information can be found using a field-deployable mobile analysis tool for extracting data from a smart phone. The difficulty comes in executing a search without damaging the phone’s memory. Since the forensic analysis tool writes an executable file to the mobile device, we’ve seen cases where that file ends up writing over evidentiary files on the phone, destroying any future value of that piece of evidence.

Establishing Protocols for Field Testing

Problems with Rapid DNA tests and the extraction of digital evidence from phones are two examples showing the difficulty of evidence collection at crime scenes. Crime scenes are often messy and chaotic, making precision and following a strict protocol even more critical.

When field tests are used, there must be protocols in place to allow law enforcement to access initial investigative leads quickly without compromising the future value of evidence. Field testing devices have to be engineered to make it as easy as possible to follow and enforce these protocols.

The devices need to capture data and documentation without requiring the end user to take extra steps. Data capture and documentation must also be done in a manner that can demonstrate tampering has not, and could not have, occurred. That engineering has nothing to do with the technical capabilities of the analytical instrument and everything to do with how the instrument is used.

Overselling and Under-explaining

Even well-meaning vendors can represent a danger when a jurisdiction goes down the road of field testing. Vendors may oversell the capabilities of their instruments or fail to fully explain their limitations. This is, after all, a competitive marketplace, and they’re trying to drive sales.

However, they are selling highly complex pieces of technology, and I believe they should be obligated to explain the limitations of a particular piece of equipment and ensure that these limitations are understood.

This can also be true when introducing new technology into a laboratory, but with their controlled environments and trained staff, labs are better equipped to understand and uncover limitations of new technologies. Forensic labs also have strict validation protocols in place that help ensure new technology produces accurate and reliable results.

Field tests create a lot of opportunities for tests to be misunderstood and misapplied if users aren’t fully aware of the limitations of the results they’re producing.

The Relationship Between Labs and Law Enforcement

The drive for more immediate results from evidence has created the demand for more field tests to be deployed within law enforcement agencies.

But, as shown by some of our results here in Houston, the long-term implications of poorly handled or compromised evidence can often have a greater impact on the laboratory. In the end, everyone is better served if evidence collection and testing don’t need to be fixed or corrected later and if stakeholders have good scientific results they can use in court.

In these disputes, it’s easy to pit lab against law enforcement. Forensic examiners and law enforcement have a long history of disputing the need for quality or speed in forensic testing, but this is often a false choice. We all want law enforcement to excel at reacting rapidly and prioritizing imminent threats to public safety. That does not have to come at the expense of considered, careful, and reliable scientific results.

In most cases, I think you’ll find that conflicts arise around testing protocols when either law enforcement or the laboratory try to do something in isolation. That’s where most field testing programs fail. Otherwise, these programs have the potential to work quite well if the two meet in the middle.

For law enforcement, it’s important to realize that the lab is not deliberately trying to work slowly; for forensic examiners, it’s important to realize that law enforcement is not deliberately ignoring quality when demanding faster results. We may have different goals, but all of our goals need to be met for the system to work appropriately.

It’s critical for a lab to understand the urgency of law enforcement, and it is just as critical for law enforcement to understand that much has to happen with evidence long after they have handed it over to prosecutors.  

For forensic scientists, it’s all about providing law enforcement accurate results as quickly as possible — or as we say here in Houston, “the right answer at the right time.”

About Notes From the Field

The National Institute of Justice (NIJ) is the research, development, and evaluation arm of the U.S. Department of Justice. NIJ aims to address the critical questions of the criminal justice field, particularly at the state and local levels.

NIJ Director David Muhlhausen developed the Notes From the Field series to allow leading voices in the field to share their strategies for responding to the most pressing issues on America’s streets today.

Notes From the Field is not a research-based publication. Instead, it presents lessons learned by on-the-ground criminal justice leaders, from years of experience and thinking deeply about criminal justice issues.

Date Published: January 5, 2021