Researching for a novel, I came across a story where the same DNA kept being discovered at a series of murders. Though the police had the ‘gold’ standard of evidence, because it didn’t match anyone in the data base, they couldn’t identify who it belonged it.

The killer remained at large, continuing his murderous ways.  As the bodies piled up, the police began to think outside of the box. Using a tool known as familial DNA, they were finally able to capture the man known as the Golden Gate Killer.

Let me explain what familial DNA is. Each person’s DNA is unique to that individual and the reason DNA is powerful evidence. When someone leaves their DNA at a crime scene, it proves they were there.

Though a person’s DNA is one-of-a-kind, the DNA of family members resemble each other. The closer the relationship, for example, parents, the more similar the DNA.  As the distance in relationships grow, say, 2nd cousins, the commonalities lessen, but are still telling.

It’s the way that commercial DNA companies are able to trace your family tree and find related people that you were unaware of.  In some cases, surprising results may upset long held believes. For example, imagine learning you had a sibling for the first time.

Looking for similarities, law enforcement is conducting searches, hoping to use the information to identify suspects in current crimes and cold cases.

Two types of searches are possible, one is of the criminal data base.  Using the samples collected from people arrested and those who voluntarily gave police their DNA, officials search to see if the DNA from a crime scene is close to one in the system.

The larger and more controversial pool of DNA records, are the genealogy data bases that the public use to find relatives and ancestors.  

In both cases, finding a relative with DNA similarities gives the police something to work with. They can look at the relations of the close match and using standard practices, investigate to see if any of them knew the victim or was in the area, etc.

How is this accomplished? In all DNA, there are genetic markers.  Technicians, focusing on twenty critical markers, run the DNA through software that compares the crime scene DNA against the data base.  

A match on half of the critical markers, strongly suggests a person is the parent, child or sibling of the suspect. Technicians who do the familial searches, provide detectives with a list of matches, starting with the closest relatives. In the California serial killer case, a match with a distant relative, led police to the murderer.

It should be noted that several DNA services, including 23AndMe and Ancestry, no longer share their data based with the police.  GEDMatch, the service detectives used in the Golden State Killer case, told members they could take down their DNA profiles if they are uncomfortable knowing police can perform searches.

The inability to access many consumer DNA sites unfortunately impacts the police’s ability to use this important tool. Familial DNA is also facing opposition from civil libertarians, who are concerned about privacy and racial profiling.

At this time only twelve states, Florida, New York and California among them, permit law enforcement’s use of familial DNA.

The reluctance to adopt the tool by states and the push back by the private sector seems a needless handicap.  Laws can be created to set guidelines about its use as the aforementioned states have done. Legislation of this type can protect citizens, while providing police the ability to use this important technology.