familial DNA
Search method using partial DNA matches to identify relatives of an unknown offender
Familial DNA is a police search method used in international criminal investigation in which, instead of an exact DNA match, investigators look for partial genetic correspondences in DNA databases in order to identify biological relatives of an unknown offender. The method is not tied to one particular legal system, but is used in a number of countries as an investigative tool in especially serious criminal cases. Where an offender's DNA has been recovered from a crime scene but produces no direct hit in existing databases, police may instead search for profiles that resemble — but are not identical to — the recovered DNA. A partial match may indicate that the person in the database is a close biological relative of the offender, for example a parent, sibling or child. A familial DNA search can therefore open a new investigative lead even though the offender has never had their own DNA profile registered.
In the BTK case from Kansas, where Dennis Rader killed ten people between 1974 and 1991, a variant of DNA kinship analysis played a decisive role. Police obtained a gynaecological sample from Rader's daughter through a court order and used her DNA to confirm that the biological material recovered during the investigation came from a close male relative. This partial match pointed directly at Rader and contributed substantially to his arrest in 2005.
Familial DNA differs in principle from conventional DNA investigation, in that the search is not directed at the offender personally but at the offender's biological network. The method therefore raises significant ethical and legal questions about privacy, since innocent family members are in effect made indirect objects of investigation without being suspects themselves. The use of familial DNA is regulated very differently from country to country. In some jurisdictions a court order is required before such a search may be initiated, while in other contexts the method is governed by administrative guidelines or is not formally regulated at all. Its effectiveness has nevertheless made it a central tool in cold case investigation internationally.
