Law enforcement investigators use a variety of tools to narrow suspects for crimes. In the case of certain crimes, such as violent crimes like murder or rape, investigators might turn to DNA evidence to determine who to charge with the crimes. In some cases, DNA evidence is used to identify victims of crimes. There are some important points everyone should know about DNA and the criminal justice system.
What kinds of DNA samples can be used?
DNA samples can come from a variety of sources. Buccal swabs, hair, fingernails and other biologic evidence contain DNA. In the case of trying to identify a person who may have committed a crime, investigators might be able to use semen samples from the crime scene or scrapings from beneath the victim's fingernails. Even evidence like fingerprints or lip prints on a glass might provide enough DNA for identification.
Is DNA always accurate?
DNA is usually accurate, but doesn't always lead to the person who committed a crime. One example of this would be if a DNA sample was collected that contained the DNA of two people, which occurs if the person has recently received a blood transfusion. Even in that case, the DNA evidence might lead to the person who may have committed the crime because the person's DNA is likely to appear predominate over the DNA of the donor.
The possibilities for using DNA to help identify who may have committed a crime or to rule people out are almost endless. Every cell in the body has DNA and almost all crime scenes contain some DNA evidence. Fighting against DNA evidence is likely to be difficult, so experienced defense representation is vital.
Source: National Institute of Justice, "DNA Evidence Basics: Types of Samples Suitable for DNA Testing," accessed April. 24, 2015