Using genealogy and genetics to solve crime

Forensic science continues to make big strides in technology and methodology.One of the latest advancements is called genetic genealogy.Also known as GG, this process combines traditional historical genealogical research with genetic analysis to study family histories.In forensics, it serves multiple uses, including identifying a victim or a perpetrator.

The process begins by extracting DNA from a specimen collected from a victim or perpetrator.This is done in a biosafety cabinet in case biohazards may be present.Next, the extracted DNA is replicated over and over so that it can be accurately analyzed – a process known as PCR amplification (polymerase chain reaction).The outcome provides a DNA profile of the victim (for human remains) or a perpetrator.

With genetic genealogy, this DNA profile is compared to a set of voluntary participants, or to millions of DNA samples on file with genealogy websites, such as GEDmatch, 23andme or Ancestry.The profiles that return partial matches are then studied for the genealogic similarities.These people are generally third, fourth, or even fifth cousins.Not many people know any relatives more distant than their second cousins.So a family history is built for each of these matches.

As the histories are built and compared, common relatives are found.The final result is a complete family tree, which allows scientists to examine each relative of the tree.Which are no longer living?Which are too young to have been the victim or committed the crime?Questions like this narrow the pool of possible matches.Eventually there is a small enough number of people that they can investigate which of those people fit the timeline of events, were in the right geographic locations, etc.

From there, detectives and forensic scientists will obtain DNA samples from living sources.In the case of identifying a victim, they will reach out to direct relatives of that person and test their DNA to see if the profile matches for a parental or sibling link.In the case of identifying a perpetrator, detectives will reach out to living direct relatives if the suspect is deceased, or go directly to the suspect for a DNA sample.That sample is then compared directly to the DNA obtained from the crime scene.If there's a match, the case is solved.

One of the most notable uses of genetic genealogy in recent history is in California.Police used DNA profiles from an online genealogy database to compare genetic profiles with their perpetrator's DNA found at the crime scene.After narrowing it to a specific few people, they start the genealogy research to find a common relative among the partial DNA matches from the database.They traced the profile back to a single relative and then gained a new DNA sample from their suspect to match against the crime scene sample.In this particular case, the match pointed to a man in the Sacramento area – they had identified the Golden State Killer, one of the most prolific serial killers in US history.

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