DNA evidence works by comparing DNA found at the scene of a crime with DNA collected from a potential perpetrator. Techniques allow investigators to make a comparison with a tiny amount of DNA.
DNA reproduces in the human body, and forensic investigators replicate this process in a laboratory to create a relatively large volume of DNA. Investigators look at specific parts of the DNA in the retrieved sample and in the sample taken from the person under investigation. Depending on the technique used, a match can reveal that a particular match is a one in a billion occurrence, which can make DNA evidence particularly compelling.