subject: Using DNA and Other Evidence to Convict a Criminal [print this page] Using DNA and Other Evidence to Convict a Criminal
By now, most people have heard of how forensic scientists use DNA and other evidence
in order to convict a criminal. In fact, in the United States it's been an integral part of several high profile court cases, and has helped to discover who committed a crime when they would have otherwise gotten away with it. DNA is also used as the determining factor in whether or not someone is the father of a child in many child support cases. Still, as prominent as this method is, very few understand exactly how one goes about collecting and analyzing DNA evidence.
Let's start with what DNA is. DNA is a molecule with long, twisted chains that are known as a double helix. While this molecule basically contains an instruction manual and blueprint for everything in your body, it's much less complex than it seems. There are only four nucleotides in this molecule - adenine, cytosine, guanine, and thymine. These nucleotides are always found in pairs that are linked together. Think of a DNA molecule as a ladder, with each nucleotide connected together just like the rungs. The only time that a person's DNA isn't completely unique to them is if they have an identical twin. This is why it's so valuable when it's presented as evidence in investigations.
In order for authorities to use this to their advantage, they have to first collect DNA at the crime scene. Have you ever seen investigators searching a crime scene and being very careful not to touch or disturb anything? That's because they're trying to keep from contaminating possible DNA evidence. They'll also require a DNA sample from each person that is a suspect. This can be obtained through blood, hair, or using a swab on the inside of the mouth. Specialists then analyze the DNA found at the scene of the crime and create a DNA profile. This profile is compared to the DNA profile for each subject in an attempt to locate a match.
Sometimes, however, there either won't be a match or there won't be any suspects for a crime. In this case, investigators can compare the DNA evidence that they're gathered with profiles that are stored in a database in hopes of finding a match. As with the original fingerprinting process, the person that committed a crime must have already submitted a DNA sample at some point in time for a match to be made.
Several of the steps involved in these methods are time consuming and meticulous, but thanks to advances in technology there are robots and various other machines that are able to handle the work involved on many of these steps.
