DNA Evidence

DNA Evidence

Alex JeffriesHistorically, fingerprints were generally considered the key individual evidence in forensic investigations. In 1985 that all changed when Alec Jeffreys applied DNA Analysis techniques to crime scene evidence to identify suspects. Using this new technique, he was able to link several samples of DNA evidence to a single person, named Colin Pitchfork, from a series of sexual assaults in the UK. Had the DNA evidence not identified Pitchfork, the wrong person would have most likely been convicted as the police had already arrested a different person for the crimes! The first person convicted using DNA evidence in the United States was a rapist from Florida in 1987 named Tommy Lee Andrews. In the next few years, "The South Side Strangler" and "The Green River Killer" were also convicted using DNA Analysis.

When entering a crime scene, investigators and officers are careful to avoid touching areas that may contain DNA evidence without gloves. To avoid contamination, they must also refrain as much as possible from releasing body fluids, such as saliva from a cough or mucus from a sneeze, while in a crime scene. DNA can be found in just about any location in a crime scene; some sources of DNA include:

Items suspected of containing DNA evidence are packaged in paper bags and sent to the lab for further analysis. They are not packaged in plastic because plastic retains moisture which can destroy or degrade DNA evidence.

  1. Weapon with skin, blood, sweat or other body tissue.

  2. Headwear such as a hat or mask which may contain hair, sweat, dandruff.

  3. Bathroom supplies such a tissue or cotton swab which may contain body fluids such as saliva, mucus, ear wax or blood.

  4. Items typically containing saliva such as toothpick, stamp, cigar/cigarette, drinking container such as a cup or bottle.

  5. Bed linens which may contain hair, skin, blood, or other body fluids.

  6. Fingernails which may have skin cells underneath them.

Items suspected of containing DNA evidence are packaged in paper bags and sent to the lab for further analysis. They are not packaged in plastic because plastic retains moisture which can destroy or degrade DNA evidence. Sunlight and higher temperatures can also degrade DNA samples, so investigators ensure that it is kept at room temperature and deliver it to the lab as quickly as possible.

Georgia Virtual, DNA Analysis, CC BY-NC-SA 3.0