What Is DNA Evidence?

One of the most reliable forms of evidence in many criminal cases is in our genes. A person's DNA (deoxyribonucleic acid) is biological evidence that can be analyzed in crime laboratories. DNA evidence can be collected from blood, hair, skin cells, and other bodily substances. It can even be used to solve old crimes that occurred prior to the development of DNA-testing technology.

This article provides a basic overview of DNA as a source of evidence in the criminal justice system.

Forensic DNA Evidence: A Brief History

The science of DNA testing was developed in 1985 by British scientist Alec Jeffreys. Genetic evidence was first tested by a forensic laboratory using his method one year later to solve a double homicide in England. It allowed law enforcement officers to link the suspect to other previously unsolved rapes and murders in the area. In 1987, a Florida rapist became the first criminal defendant in the United States to be convicted through DNA.

As DNA became the gold standard for identifying criminal suspects, law enforcement agencies took note. The FBI and police departments throughout the U.S. started assembling DNA databases such as the Combined DNA Index System (CODIS). 

In addition, sex offenders in all states are now required to submit DNA samples to their local police department. Many states make use of DNA evidence even in criminal charges involving misdemeanors, although many crime labs are overwhelmed with backlogs of genetic samples and may be unable to process them in a timely fashion.

How Does DNA Testing Work?

A sufficient amount of DNA may be found in virtually any type of biological material. For violent crimes, such evidence typically comes from blood or other bodily fluids. Hair and skin cells left at the crime scene also may provide investigators with enough DNA for testing purposes.

DNA evidence is analyzed using the polymerase chain reaction (PCR) method. This allows for very small samples to be tested and identified. Once the sample is tested, it may be cross-referenced with DNA profiles already in a database or with genetic data provided by a suspect.

While DNA testing is not completely foolproof, it is more than 99% accurate. In fact, there is only a one in one billion chance that the DNA test results of two individuals will match. Errors in testing are often the result of mix-ups in the lab or the contamination of samples. In addition, each state has specific rules for DNA sample collection and handling. Courts might not allow the use of genetic evidence in court if these requirements are not met.

Other Uses of Genetic Evidence

Genetic material preserved in evidence lockers has many applications. In addition to criminal investigations, DNA analysis can also be used to exonerate wrongly accused individuals. That includes those who were victims of wrongful convictions for violent crimes like sexual assault. This is important for those convicted solely on the basis of eyewitness testimony, which is not always reliable. More than 575 people have been exonerated through post-conviction DNA tests.

DNA court orders can also be used to determine paternity in child support cases. In the world of forensic sciences, DNA technology can also be used to:

• Identify the remains of crime and accident victims
• Conduct genealogical research

Keep in mind the disclaimer that a DNA match will not necessarily result in securing a convicted offender. Like all other evidence, DNA testing is subject to chain of custody and tampering issues.

Learn More About DNA Evidence From a Defense Lawyer

Is DNA evidence being used against you in your pending criminal case? Are you curious about the logistics of a DNA-based prosecution? In these situations, consider a client relationship with defense counsel. You can learn more by contacting a local criminal defense attorney. They will be able to provide legal advice on the criminal law concepts of DNA testing, accuracy, and more.