What You Need to Know About DNA Evidence

DNA evidence is playing a larger role than ever before in criminal cases throughout the country, both to convict the guilty and to exonerate those wrongly accused or convicted. This increased role places greater importance on the ability of victim service providers to understand the potential significance of DNA evidence in their clients' cases.

What Is DNA?

DNA, or deoxyribonucleic acid, is the building block for the human body; virtually every cell contains DNA. The DNA in people's blood is the same as the DNA in their saliva, skin tissue, hair, and bone. Importantly, DNA does not change throughout a person's life.

The Value of DNA Evidence

DNA is a powerful investigative tool because, with the exception of identical twins, no two people have the same DNA. Therefore, DNA evidence collected from a crime scene can be linked to a suspect or can eliminate a suspect from suspicion. During a sexual assault, for example, biological evidence such as hair, skin cells, semen, or blood can be left on the victim's body or other parts of the crime scene. 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 FBI's Combined DNA Index System (CODIS) to identify a suspect anywhere in the United States or to link serial crimes to each other.

The effective use of DNA as evidence may also require the collection and analysis of elimination samples to determine the exact source of the DNA. Elimination samples may be taken from anyone who had lawful access to the crime scene and may have left biological material. When investigating a rape case, for example, it may be necessary to obtain an elimination sample from everyone who had consensual intercourse with the victim within 72 hours of the alleged assault to account for all of the DNA found on the victim or at the crime scene. Comparing DNA profiles from the evidence with elimination samples may help clarify the results.