How is genetic evidence used in court?

Convincing evidence is required for prosecutors to obtain convictions. Allegations must be substantiated. DNA evidence can provide proof the state needs to link a Milwaukee defendant to a sex crime or show a person is wrongfully accused.

Human cells hold identifying information carried by deoxyribonucleic acid or DNA. Like fingerprints, each person’s characteristics mapped out in DNA are unique. Police investigators can trace the “owner” of DNA by conducting tests on cell-containing evidence left behind after a sexual assault.

Genetic codes are revealed in traces of skin tissues and body fluids like blood, semen, and saliva which can be gathered at a crime scene or from a sexual assault victim. Investigators can tie DNA evidence directly to a defendant or, when a sexual offender is unknown, compare test results with existing DNA profiles housed in a federal database known as the Combined DNA Index System or CODIS.

Sex crimes often have few if any witnesses. DNA can supply additional proof in cases where the only other evidence available may be the accounts of the alleged victim and defendant. In the same way DNA can place a defendant at a crime scene a lack of evidence can absolve a person of any wrongdoing.

People other than the defendant sometimes are required to undergo DNA tests – investigating officers, witnesses and a purported victim’s consensual sex partners included — to eliminate the possibility someone else was involved in a crime. DNA collected during an investigation is added to the CODIS database, whether or not test subjects are charged with or convicted of a sexual offense.

Criminal defense attorneys advise DNA can place a defendant at a crime scene, but it cannot pass on details about events that happened there. The genetic information is only a marker. Prosecutors must make the connection between DNA evidence, even identifying information found in semen, and a sexual assault.

Source: Rape, Abuse and Incest National Network, “The Importance of DNA in Sexual Assault Cases,” accessed July 08, 2015