The use of DNA evidence in criminal investigations has grown in recent years. DNA testing has helped law enforcement identify criminals and solve difficult crimes. On the other hand, DNA evidence has helped prove that many convicted people are actually innocent.

Although DNA evidence can be very accurate, there is the danger of the evidence being compromised. Law enforcement must take great measures during the collection process to not contaminate the evidence. Since many crime scenes may have only very small samples of DNA, any contamination of the evidence could jeopardize identifying the criminal and solving the crime.

What Is DNA?

DNA, or deoxyribonucleic acid, contains all the genetic information about a person. It's the instructions for the body's entire genetic makeup. DNA is unique to each individual person. A person has the same DNA throughout his entire body, and it's located in every cell. Cells are the basic building blocks of all people.

Where Can DNA Be Found at a Crime Scene?

Since a person's DNA is located throughout his entire body, any materials left from his body at a crime scene will contain his DNA. Some examples of bodily materials that contain DNA evidence include:

  • Blood
  • Saliva
  • Perspiration
  • Hair
  • Teeth
  • Mucus
  • Fingernails
  • Semen

DNA evidence can be found almost anywhere at a crime scene. Only a small amount of human cells are sufficient to provide DNA evidence that will help solve a crime. Much of the evidence may be found on a crime victim. Some examples of places where DNA evidence may be found include:

  • Cigarettes
  • Clothes
  • Stamps
  • Bite marks
  • Weapons
  • Cups
  • Tissues

How Is DNA Collected at a Crime Scene?

DNA evidence can be easily contaminated during collection and storage. Contamination can occur when DNA evidence mixes with the DNA of another person. Law enforcement must make sure they take all precautions to not compromise the evidence. Examples of precautions that officers should take include:

  • Wearing gloves
  • Avoiding coughing or sneezing on the DNA evidence
  • Preventing the storage of DNA evidence in direct sunlight or a warm setting
  • Using paper bags or envelopes for storage and not plastic bags

DNA evidence usually must be stored at room temperature. Paper bags should be used because plastic bags will retain moisture that may damage the evidence.

How Is DNA Used in Criminal Investigations?

Since every person has unique DNA, the discovery of particular DNA evidence at a crime scene can help law enforcement determine who was involved in the crime. On the other hand, law enforcement can determine that a particular suspect wasn't involved by the absence of his DNA.

The technique used by law enforcement to identify people based on their DNA is called DNA profiling, or genetic fingerprinting. DNA profiling is highly accurate as long as the evidence isn't contaminated. Many of the DNA samples go into the Combined DNA Index System (CODIS), a national DNA database that's funded by the Federal Bureau of Investigation. CODIS can be used to identify possible suspects by matching DNA profiles. This database can help forensic crime laboratories at the local, state and federal levels work together to identify criminals and solve crimes.

Questions for Your Attorney

  • If I am arrested for a crime, do the police have the right to order me to provide a DNA sample for their criminal investigation?
  • If a family member commits a crime, can his DNA at the crime scene lead law enforcement to wrongly believe that I committed the crime? How similar is DNA among family members?
  • What procedures can I take if I believe that DNA evidence found at a crime scene was accidently contaminated by police during the collection process?

Tagged as: Criminal Law, DNA evidence, criminal investigation, criminal lawyer