A primer on DNA forensics

DNA

Deoxyribonucleic acid, “the building block of life,” has become a standard for forensic evidence. The famous “double helix” molecule is unique to each person with the exception of identical twins. DNA is shed at crime scenes through hairs, blood, semen, saliva — virtually any biological matter. It is very stable, meaning even old and degraded samples can be analyzed and compared. Once considered mysterious and suspicious, DNA evidence is now a routine part of the judicial process.

The history

The first forensic use of DNA occurred in England in 1983, when samples from a murder and sexual assault exonerated the main suspect in the case. Three years later, DNA from a second murder was used to link the crimes and convict a different man. In Canada, DNA was first used in 1987 in the case of the “Spandex rapist” who had attacked seven women in Edmonton. But the sample available for testing proved too small to give a reliable result and the suspect was acquitted. (The man was convicted 20 years later when DNA linked him to a separate sexual assault “cold case” in Calgary.)...