How is DNA Used in Criminal Investigations?


A person’s genetic information is recorded in their DNA, also known as deoxyribonucleic acid. Each person’s body contains a distinctive and different DNA sequence from each other. Because DNA is found at a cellular level, a very small sample will be enough to identify a person’s sequence and subsequently identify a specific person. Because of its unique makeup, law enforcement agencies have embraced the criminal applications of DNA.

DNA evidence can be extremely accurate. However, law enforcement personnel must take proper precautions to not contaminate the DNA samples. Any contamination will affect the accuracy of the samples and may result in an innocent person being convicted.

Crime Scene Collection of DNA

At a crime scene, a forensic team will comb the area for possible DNA evidence. DNA can be collected from bodily fluids or other materials. DNA may be pulled from any of the following items:

  • Hair
  • Blood
  • Skin
  • Mucus
  • Saliva
  • Fingernails
  • Semen

Generally, at a crime scene the vast majority of DNA will be discovered on the body of the victim. Many victims will have the attacker’s DNA underneath their fingernails, inside of their mouths or elsewhere on their person. However, DNA may also be found on a weapon, such as the trigger of a gun or on a cigarette that the attacker threw away.

When DNA is collected from a crime scene, the collectors must wear gloves to avoid contamination. Further, the samples should be stored in a paper container as opposed to plastic. Plastic containers may contain moisture which will affect the samples.

How Do the Police Use Collected Samples?

The presence of DNA at a crime scene will help law enforcement officials to determine who was present at an actual crime scene. The presence of a person’s DNA does not necessarily mean that he committed that crime. However, it does mean that a specific person was present.

Law enforcement officials use DNA profiling to identify the person to whom the DNA belongs. DNA profiling may also be called genetic fingerprinting. After a forensics team collects a DNA sample, it is placed into the Combined DNA Index System. The Combined DNA Index System (CODIS) consists of a national database of DNA samples which is maintained by the FBI. The database uses DNA samples which connect various samples taken from local, state and federal crime scene investigations. Because different agencies from across the country contribute to the CODIS, the effectiveness of the CODIS greatly increases.

For more information on DNA and how it can affect the outcome of a criminal case, contact attorney Mario Madrid at 713-877-9400.

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