DNA Testing in Criminal Prosecutions

DNA, also called deoxyribonucleic acid by scientists, is often used as important evidence by prosecutors in criminal law trials. DNA is a set of molecules found in the human body. Similar to a fingerprint, each person in the world has a different and unique DNA profile. Because each person’s DNA profile is different, DNA matches can be used by criminal prosecutors to help prove to a jury that the suspect facing criminal charges is most likely the person who is guilty of committing the crime.  

DNA can unknowingly be left behind by a suspect at a crime scene and later discovered, tested, and analyzed by careful investigators.  DNA is found in blood, hair, saliva, teeth, fingernails, skin cells, and bodily fluids including semen. Crime scenes where DNA is commonly found are typically places where violent crimes occurred, including rape, murder, kidnapping, and other incidents involving physical confrontations.

If a suspect’s DNA is found at a crime scene, scientists and law enforcement officials can gain access to a national DNA database that is filled with DNA samples taken from criminal offenders. The DNA database, called the Combined DNA Index System, is used to compare a suspect’s DNA to the DNA of hundreds of thousands of convicted criminals.

This process is sometimes called DNA profiling. If a DNA match is found by law enforcement officials, the prosecution will use this information as evidence to try to prove that the suspect on trial is the person who committed the criminal act.

Finding DNA at a crime scene does not always lead law enforcement agents to find the person who is guilty of committing a crime. In some cases, a person’s DNA may be found at a crime scene, but that person was not involved in committing the crime.

Sometimes, a DNA sample may be incomplete, damaged by age or weather, or mishandled by investigators. In these cases, the DNA sample is considered to be inconclusive evidence and might not be used by criminal prosecutors.

How Can Law Enforcement Officials Get Samples of a Suspect’s DNA?

Law enforcement officials may be able to get samples of a suspect’s DNA if a suspect has not already been found in the national DNA database. In some states, people that have been convicted of crimes are required by law to provide law enforcement officials with DNA samples. This requirement is called mandatory DNA sampling. The laws regarding mandatory DNA sampling vary by state and crime. The types of crimes that typically require mandatory DNA sampling are mostly violent crimes and felonies including murder and rape.

In other cases, a suspect may give law enforcement officials permission to take a DNA sample from them. DNA samples are typically taken from suspects in the form of a saliva swab or blood test. If a suspect is eventually found to be innocent of the crime, they may request that their DNA sample be removed from the national DNA database.

If a suspect refuses to give a DNA sample, law enforcement officials may be able to obtain a DNA sample by collecting everyday items that were used by a suspect.  DNA may be collected by taking saliva samples from a used cup, or hair and skin samples from a hairbrush or razor.

Can DNA Evidence Prove that a Suspect Committed a Crime?

The prosecutors in a criminal case will often argue that DNA evidence proves that the suspect committed the crime. This is especially common if a suspect’s DNA is found on other forms of important evidence, such as a murder weapon or on materials used to transport a body such as bedding. Sometimes, a jury will determine that DNA evidence by itself is not enough evidence to prove that a suspect is guilty of a crime.   

A suspect’s defense attorney may argue that the suspect is innocent because the DNA evidence is inaccurate or incomplete. In these cases, the defense may be able to convince the jury that the suspect is not guilty of committing the crime. The suspect’s defense attorney may also argue that there is a small percentage of probability that the DNA evidence belongs to someone other than the suspect.

Should I Contact an Attorney Regarding DNA Testing?

If you have been charged with a crime, you may be able to defend yourself against the criminal charges, but this is a complex and difficult task. For the best outcome in your case, you should strongly consider contacting a criminal defense attorney as soon as you have been arrested or charged with a crime.

There are many complicated factors that go into defending a suspect against criminal charges. An attorney can explain your rights to you and help you determine if it’s in your best interest to take a DNA test.