CSI Toolkit – DNA Evidence

Ever since the O.J. Simpson murder trial the American public has had a certain level of familiarity with DNA profiling. This is the process used to match the DNA profile of a known substance to the DNA profile of a sample that a scientist would like to identify.

For example, the in the case of O.J. Simpson the prosecution looked to show that the DNA found at the scene of the crime matched that of Simpson.

DNA profiles are encrypted sets of “letters” which vary slightly from person to person. Though these profiles are 99.9% the same in every human, the tiny differences play a huge role both in the individuation of each person and in helping forensic professionals to distinguish one person from another.

Sir Alec Jeffreys, of the University of Leicester in England, first reported the techniques used in DNA profiling in 1986. Now, DNA testing makes up a vital part of the identification processes in law enforcement activities across the Western world.

CSI professionals look for samples at a given crime scene, which many contain viable DNA. These samples may be hair, blood, tissue, skin, or other bodily samples.

However, the location of a DNA sample that positively matches that of a suspect or victim does not necessarily mean that that person was present at the crime scene. In certain cases DNA evidence was found to have been faked, as the true criminals planted the DNA of others at the crime scene.

In one notable case, Dr. John Schneeberger raped one of his patients and initially escaped detection by using a technique to fill his arm with blood from another person, so that when investigators drew his blood it did not match that of the perpetrator for which they were searching.