In identifying the perpetrator of a crime, major tasks might include sifting through the evidence for materials having characteristics that do not change over time.
Fingerprints are examples of such characteristics. Another example of profiling technology is trace DNA (deoxyribonucleic acid). What is this and where do investigators find it?
A little background
A technique called a polymerase chain reaction, or PCR, sometimes known as “molecular photocopying,” is essential to performing DNA analysis on a minute scale. For example, this technique enables researchers to compare individual human hairs or to identify the badly charred remains of people who died as the result of a fire or a mass disaster. “Trace DNA” refers to microscopic amounts of DNA transferred through skin contact.
Case in point
To illustrate, a murderer strangled his victim using the rubber electrical cord from a vacuum cleaner. The examiner divided the cord into four zones, which were then processed individually. The two center zones gave up DNA profiles that matched the DNA of the victim. The two outside zones showed mixed profiles that included the DNA of the suspect.
Sources and issues
From items dropped and left behind at a crime scene to food items with bite marks and fixed items such as steering wheels, there are countless sources that can go into DNA profiling. Wide-ranging examples include the brim of a baseball cap, a cigarette butt, an ignition switch, a drinking straw, toothpicks, socks, an envelope and a chicken wing. Hair and fibers provide much of the trace DNA examiners use. However, errors can result during the collection and analysis of such evidence due to transfer, contamination or even the evaluation of the data collected.