Every week it seems, another Jane or John Doe has been identified. Another man named as a killer or rapist from years earlier. Another case closed. That is the power of investigative genetic genealogy.
Most genetic genealogists do not work in an accredited forensic laboratory, and do not testify in court. Their work is "investigative," meaning it produces something like a tip. Law enforcement then confirm the tip forensically, having an accredited private lab or government crime lab perform a forensic comparison of the suspect's DNA to the crime scene DNA. (Our lab, Intermountain Forensics, can perform all of these steps - genetic DNA testing, forensic DNA testing, and genetic genealogy.)
Our lab, Intermountain Forensics, has elected to use DNA equipment from Verogen, owner of the public DNA database GEDMatch. Consequently, our genealogical DNA profiles are designed for upload to GEDmatch.
Once uploaded to GEDmatch, a DNA profile produces "matches" to profiles uploaded by or on behalf of potential relatives. Some matches are distant, such as 4th or 5th cousins. Others might be quite close, such as a half-brother or first cousin. The closer the match, the easier it is to trace the match's genealogy and determine how the suspect might be related to the match.
Once a list of matches to the suspect's DNA has been generated on GEDmatch, the genealogist narrows it down. For example, if the suspect is male, then female matches can be eliminated. Males of a certain age may be eliminated. Attention may turn to males with opportunity - who, for example, lived near the victim at the time of the murder.
As mentioned above, once a genetic genealogist identifies a potential suspect, law enforcement must confirm it. Whether voluntarily or by ruse, a sample of the potential suspect's DNA will be obtained, and a forensic lab will compare it to the crime scene DNA.