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Genetic genealogy uses a comparison of DNA testing with genetic databases to construct a reverse family tree to locate a suspect otherwise unknown to investigators, has emerged in recent years as law enforcement’s most powerful tool.

All it takes is a single strand of DNA to solve decades-old cold cases and identify suspects in current ongoing investigations.

DNA is extracted from something like a tooth or a fingerprint left on a car door handle and uploaded to a massive database, where it is compared with millions of other DNA profiles for similarities, known as "starting data points." Those points are then used to build a family tree for each person.

"We look at the genetic relatives of our unknown sample," genetic genealogist Misty Gillis, of Identifinders International and BirthParentFinder explained in an interview, "It gives us a list of all the DNA matches that they have, and it tells us how much DNA is shared with that person, an estimation of what their relationship could be with that person, whether it’s a first cousin, a second cousin or a third cousin."

Gillis continued, "We can use that information to be able to build out and identify who they are."

Idaho murders

Genetic genealogy played a key role in finding Bryan Kohberger, accused of murdering 4 college students. Last November Madison Mogen, Kaylee Goncalves, Xana Kernodle, and Ethan Chapin, were killed in Moscow, Idaho.

The Idaho murders have been a high-profile case. DNA was found on a knife sheath left at the scene of the murders.

According to sources, Idaho police were able to make significant progress in the case thanks to this cutting-edge DNA analysis.

The power of genetic genealogy was previously demonstrated in 2018 when it led to the identification. And the arrest of Joseph DeAngelo, aka the Golden State Killer.  After decades of evading justice for a string of crimes, including murders and rapes throughout California, DeAngelo was finally apprehended. 

Paul Holes, a former investigator with the Contra Costa County Sheriff's Office specializing in cold cases, praised genetic genealogy for its role in narrowing down a vast pool of suspects in the case.

By analyzing common ancestors and constructing an extensive family tree, investigators were able to zero in on potential suspects, ultimately leading to DeAngelo's arrest.

Genetic genealogy has privacy concerns

The databases used by genealogists rely on voluntarily submitted DNA profiles from individuals who have taken tests with private ancestry-tracing companies. While some companies openly share this information, others require a subpoena.