NCJ Number
205071
Journal
Law Enforcement Technology Volume: 31 Issue: 3 Dated: March 2004 Pages: 108,110,112,113
Date Published
March 2004
Length
4 pages
Annotation
This article discusses the issue of crime scene DNA contamination and reports the results of a recent United Kingdom study on the potential DNA contamination of crime scenes.
Abstract
Increasingly sensitive tests are continuously being developed that can detect human DNA from various cellular sources. While this helps the criminal justice system locate and prosecute offenders, it also increases the possibilities of DNA contamination at crime scenes and in forensic laboratories. Seemingly harmless movements by crime scene investigators such as scratching a nose or shaking a head is enough to deposit their own DNA at the crime scene, thus contaminating the scene and any samples taken for analysis. The 2003 issue of “International Journal of Legal Medicine” contained a study from the United Kingdom in which researchers tested the amount of crime scene DNA contamination left by investigators under controlled conditions. The experiments had four treatment conditions: “no movement,” “movement,” “coughing,” and “talking.” During each test, the subject would mimic movements that a crime scene investigator would use to collect evidence, such as small arm movements and turning the head. Each experiment was performed in both a standing and kneeling position, with and without protective clothing, including a face mask. The results showed that no DNA contamination was introduced for the “no movement” condition. However, when normal crime scene movement was introduced, a high rate of contamination was found when no protective clothing was worn; enough contamination to produce a full DNA profile of the test subject. However, in experiments with protective clothing, although DNA contamination still occurred, it was greatly reduced, suggesting that protective clothing should be used for crime scene investigations and that care should be taken to minimize movements at crime scenes. Furthermore, care should be taken in the type of mask worn to reduce respiratory particle fallout. Within a forensic laboratory, DNA contamination has been minimized by wearing face masks and enforcing a no talk rule while in the laboratory. Other precautions include minimizing access to crime scenes and requiring police officers to be trained in how to minimize DNA contamination, including patrol officers who may be the first officers at a crime scene.