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Forensic Services Manual

DNA evidence plays a crucial role in criminal cases throughout the country. DNA stands for deoxyribonucleic acid and is the building block for the human body, as virtually every cell contains DNA. This type of evidence is used in court cases in order to convict the guilty, to eliminate suspects, and to exonerate those wrongly accused. As no two people in the world contain the same DNA (with the exception of identical twins), DNA is a valuable investigative tool in linking (or eliminating) individual suspects from suspicion. For example, during a sexual assault, biological evidence such as blood, semen, hair, or skin cells can be left on the victim’s body or other parts of the crime scene. If properly collected, DNA can be compared with known samples to place a suspect at the scene of the crime. In addition, if no suspect exists, a DNA profile from crime scene evidence can be entered into the Federal Bureau of Investigation’s Combined DNA Index System (CODIS) to identify a suspect anywhere in the United States. As DNA evidence grows increasingly fundamental to court cases, it is essential to recognize not only the overall importance of DNA, but also identify protocols and methodology involved in effective DNA evidence collection.


Evidence Collection


Medical personnel, such as victim service providers, crime scene technicians, and nurse examiners should be aware of important issues involved in identifying, collecting, transporting, and storing DNA evidence. DNA evidence should be identified immediately at the crime scene; otherwise, it may not be collected, or it may become contaminated or degraded. According to the FBI’s Trace Evidence Recovery Guidelines, once a case is initiated, a file specific for that case must be immediately created. Documentation of questioned and known evidence collection, whether completed in a laboratory or at a scene, must include detailed notes on the following: the date and time of the collection, the name of person or persons collecting the evidence, a descriptive listing of item or items collected, an identifier for each item collected, such as an item number or case number, and the location of each item, which may be recorded by notes, sketches, measurements, or photographs.


Prevention of Contamination and Loss

While collecting and examining items, proper guidelines and techniques must be followed in order to avoid contamination or loss of evidence.  Contact between items and personnel before the appropriate trace evidence has been secured should be monitored and restricted as much as possible. Appropriate protective apparel, such as laboratory coats, disposable gloves, and protective eyewear, must be worn to avoid contamination from the clothing of the examiner. If necessary, apparel must be changed to avoid contamination between evidentiary items, locations, and personnel. Items must be collected, packaged, and sealed individually in appropriate packaging. Items must also be kept in a secure, sealed package until the item is processed in a controlled environment.


Equipment and work surfaces used during the evidence collection and examination process must be sufficiently cleaned before analysis begins and continued as often as necessary in order to prevent contamination. Evidence examination areas should have proper lighting, easily cleaned surfaces, and a physical environment conducive to restricting excessive air currents, static electricity, and general foot traffic. Any contact, condition, or situation that could cause contamination or otherwise compromise the examination must be documented and communicated between the laboratory analyst or analysts and the submitter


Detection, Collection, and Preservation Techniques

Trace evidence recovery or collection techniques utilized should be done so carefully and directly, with the least intrusive protocols applied. Collection techniques include picking, lifting, scraping, vacuum sweeping, combing, and clipping, and each technique must use the proper instruments, such as clean forceps, adhesive bearing substrates, spatula, and vacuum cleaner with filter trap, comb or brush, and clean, sanitized scissors. All evidence packages must be properly sealed. Small or loose trace evidence must be secured in clean, unused primary containers such as paper packets or petri dishes. The primary container should then be secured in an envelope or paper bag. Clothing and other items that are wet should air dried as soon as possible, without exposure to heat or sunlight. An arrangement to collect any trace evidence that may fall from the item during drying should be used.



Handbook of Forensic Service- This PDF provides an introduction to the forensic services offered by the FBI as well as detailed information on the following: submitting evidence, evidence examinations, crime scene safety, and crime scene search. In addition, this PDF provides a helpful index in order to look up information on specific forensic topics.

The FBI DNA Laboratory- This comprehensive PDF from the Office of the Inspector General provides a review of protocol and practice vulnerabilities in DNA collection and analysis. In addition, this resource presents a specific case in which guidelines and procedures were compromised during the collection process and the effects of these errors upon the court case.

FBI Laboratory Services: CODIS- This resource offers information on the Quality Assurance principles and practices the FBI maintains in its DNA database. Find out more about effective procedures and read about the DNA Identification Act of 1994, the Standards for DNA Forensic Testing Labs, and Standards for DNA Databasing Labs.

DNA Forensics- Sponsored by the Human Genome Project, this resource presents a comprehensive overview on several DNA Forensics topics, including DNA typing, technology, and ethical, legal, social issues with DNA Databanking.

Crime Scene Survey Course- One of the services the FBI provides for federal, state, and local law enforcement agencies. Features of this course include instruction on preparing basic crime scene diagrams, an overview of tools and equipment available to aid in the documentation of the scene, how to survey and document crime scenes, and formulas related to crime scene mathematics.

Explore Forensics- This website provides useful introductory information on the field of forensics. It also covers the different kinds of evidence, evidence collection and analysis, and an online book of selected case studies.