DNA Profiling


DNA stands for deoxyribonucleic acid. This is the name of the chemical which is found in virtually every cell in the human body and which carries genetic information from one generation to the next. Just like fingerprints, humans each have a unique DNA signature that remains unchanged throughout their lives. Whereas fingerprints can only be found at a crime scene if a person touches a suitable surface with bare fingers, DNA can be extracted from hairs, skin cells, blood, fragments of bone, or teeth, as well as body fluids left at a crime scene. DNA testing, generally called DNA profiling, takes advantage of the fact that, with the exception of identical twins, the genetic material of each person is unique and is an omnipresent residue that trails us wherever we go. A DNA profile is simply a unique set of numbers obtained from a person’s DNA that acts as a personal identification number’. In cases where traditional fingerprints are not found, DNA profiling may provide the answer to the question: Who was present at a crime scene? These physical properties of DNA have made it a critical tool in fighting crime.

Throughout the world, DNA profiling provides evidence that may be used to convict criminals. It also enables forensic scientists to re-examine old cases, previously closed due to lack of evidence. Cold cases have been re-opened because DNA profiles are now able to be extracted from stored crime scene samples and evidence. These cases have not always been solved, but the use of DNA evidence has allowed many prisoners who were originally found to be guilty, to now be exonerated, when DNA tests proved their innocence.

This technique was also indispensable in identifying victims of the bombing of the World Trade Center on 11 September 2001 and the identification of bodies after the Tsunami on 26 December 2004, as well as of apartheid activists buried, alone or in mass graves, in South Africa.

EvidencepreservationIn the USA an organization called The Innocence Project has been set up to assist in the exoneration of wrongfully convicted people, through the use of DNA testing. The organisation was founded in 1992 and to date has been instrumental in successfully exonerating 272 people, 17 of whom served time on death row. The average sentence served by those exonerated by DNA has been 13 years in prison, before their exoneration and release. In all these cases, DNA testing has provided irrefutable proof of wrongful convictions, as well as provided invaluable links to the actual perpetrators of the crimes.

Because individual DNA is as personal as a fingerprint, DNA collected from a crime scene can either link a suspect to evidence or eliminate a suspect. When evidence from one crime scene is compared with that from others, the crimes can be linked nationwide, thereby providing valuable criminal intelligence information to the police and/or evidence for use in court. As DNA retains its integrity, evidence from crimes committed years previously may yield sufficient DNA for analysis and point to a previously unknown suspect.

DNA profiles may be used to:

  • Identify potential suspects whose DNA matches evidence found at crime scenes.
  • Exclude a suspect quickly, by demonstrating that a person was not involved in a particular crime scene or crime.
  • Identify patterns of criminal behaviour through matching DNA profiles found at several crime scenes; this may help solve past, current and even future crimes. In other words, not only will DNA profiling increase the likelihood of identifying unknown perpetrators, but it will also increase the possibility of linking perpetrators to multiple crime scenes.
  • Promote plea bargains, when suspects are confronted with real evidence in the form of a DNA match. For example, in Britain, 85 percent of suspects plead guilty when presented with a match of their DNA to the crime.
  • Exonerate persons wrongly accused of crimes.
  • Identify victims of disasters.
  • Establish paternity and other familial relationships.
  • Identify endangered and protected species when wildlife officials wish to prosecute poachers.
  • Detect and identify micro-organisms polluting the air, soil or water.