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Collecting DNA Evidence at Property Crime Scenes

Types of Evidence

Introduction to Types of Evidence

The field of crime scene processing is extremely demanding and ever changing. Demands from the scientific and legal communities influence the crime scene investigator's everyday activities. The scientific community focuses on the examination of evidence collected at a crime scene. Investigators and crime scene specialists are responsible for identifying, securing, documenting and preserving biological evidence recovered from a crime scene. Legal considerations include scrutiny of procedures used at crime scenes and chain of custody. The investigator must also know when and how to make decisions to obtain written consent or a search warrant to assure that the evidence will be admissible in court and not subject to a motion to suppress. DNA databases provide law enforcement officers with the ability to identify potential suspects when no prior suspect existed. The development and expansion of databases that contain DNA profiles at the local, state and national levels have greatly enhanced law enforcement's ability to solve cases with DNA evidence. These databases are operated using the Combined DNA Index System (CODIS), a software program that permits the cross-comparison of DNA profiles developed from biological evidence found at crime scenes and also of known offender profiles. This training describes handling the most common types of biological evidence that may be encountered. This general information is subject to agency protocols for handling evidence.

Learning Objectives on the Types of Evidence Module

Upon successful completion of the four modules of training, the student should be able to do the following:

  • Describe the types of physical evidence typically encountered at a property crime scene.
  • Define Locard's Exchange Principle.
  • Describe types of trace and biological evidence.
  • Define "touch DNA" evidence.
  • Explain the importance of maintaining the integrity of physical evidence.
  • List and describe the three types of crime scenes.
  • Describe the process used to secure and investigate a crime scene.
  • Describe the purpose of a victim interview.
  • Describe methods used to locate evidence at a crime scene.
  • Describe the importance of scene documentation in successful case resolution.
  • Define priorities for collecting biological evidence.
  • Define situations that require control and reference samples to be collected.
  • Describe equipment used when collecting biological evidence.
  • Describe procedures used to collect, mark and package wet and dry biological evidence.
  • Describe the purpose and method used to establish and maintain the chain of custody for items of evidence collected at a crime scene.
  • Describe the methods used to preserve evidence.
  • List the elements included in a crime scene report.
  • Describe general requirements for an investigator when testifying in court.
  • Describe the purpose and use of DNA databases.
  • List the different types of DNA profiles in CODIS.
  • Describe the purpose of a "John Doe" DNA warrant.

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