forensic genealogy

Forensic genealogy is an investigative method in which a DNA trace from a criminal case is compared with information in DNA-based genealogy databases in order to identify an unknown perpetrator or an unknown victim. The method works by searching for genetic relatives of the person whose DNA was found at the crime scene. Once possible relatives have been identified in the database, investigators map family trees and public records to narrow down the circle of possible suspects.

The method gained international attention with the solving of the Golden State Killer case, in which Joseph DeAngelo was identified in 2018 after decades of investigation precisely by means of forensic genealogy. A DNA trace from the crime scenes was matched against relatives in a public genealogy database, which made it possible to point to DeAngelo as a suspect. In Danish the method is also referred to as genetic genealogy (genetisk slægtsforskning).

It is important to stress that the method does not in itself constitute criminal evidence, but functions as an investigative tool that can direct the authorities towards a specific suspect. A traditional forensic genetic DNA match will typically follow the identification and form the basis for the actual assessment of evidence in court.

In Denmark, the Danish Parliament (Folketinget) has adopted separate rules on the police's access to use forensic genealogy as an investigative measure. This reflects that the method raises particular legal and ethical questions — including the protection of personal data concerning those relatives whose genetic data is used indirectly without them being suspects themselves.