' Familial DNA Searches and Criminal Investigations | MTTLR

Familial DNA Searches and Criminal Investigations

From 1975-1986 the notorious Golden State Killer committed 12 murders, 45 rapes, and 120 burglaries across 6 California counties. These crimes remained unsolved until 2018 when police arrested Joseph DeAngelo, a 73 year old United States Navy Veteran and police officer, in his home in Citrus Heights, California. DeAngelo’s crimes were finally solved after all of these years through the use of a novel forensic technology: familial DNA search (FDS).

In a traditional DNA search, law enforcement gather DNA material left at a crime scene. They then test that sample to see if it matches the DNA of anyone in a vast database of known offenders, like the FBI’s combined DNA Index System (CODIS), who have previously provided a DNA sample. This type of search couldn’t help solve DeAngelo’s murders though. The traditional search requires a perfect match between the sample DNA taken from the crime scene and someone’s DNA from the database. Since DeAngelo had never been convicted of a crime, he had never given a sample to be entered into CODIS so there was no perfect match for the DNA he left at the scene.

In contrast, FDS allows law enforcement officers to analyze DNA samples from a crime scene for imperfect matches of family members from within a DNA database. Here is a simplified explanation of the process. Since DNA is inherited, family members will contain more shared genetic markers than non-related individuals do. As such, if law enforcement finds two sufficiently similar matches, they can, with a reasonable degree of probabilistic certainty, conclude that the two individuals are related.

So, using FDS, if law enforcement runs a crime scene DNA sample through a database and finds an imperfect DNA match from a known individual, they can presume that the perpetrator of their crime is a relative of this known individual. They can then focus their investigation by narrowing their list of suspects to members of this individual’s family tree.

In DeAngelo’s case, the officers investigating his then unsolved murders created a profile on a website called FamilyTreeDNA; a platform that purports to connect its users with long lost relatives using familial DNA analysis. The officers then submitted DNA samples from a Golden Gate Killer crime scene rape kit to their profile and found a close familial match. Once they had their match they were quickly able to hone in on DeAngelo, a relative of this match, since he was about the right age and they had long suspected that the Golden State Killer was ex-law enforcement. DeAngelo was arrested shortly after. He has since pled guilty to 26 counts of murder and kidnapping and is currently serving 26 consecutive life sentences in a California prison.

Because DeAngelo pled guilty before trial, his defense counsel never challenged the officer’s use of FDS as a violation of DeAngelo’s 4th Amendment protection against unreasonable searches and seizures. However, his arrest sparked fierce debate about the legality and the wisdom of allowing law enforcement carte blanche use of FDS to solve cold cases. Proponents see FDS as a powerful new tool for law enforcement and believe that so long as they are innocent, they have nothing to fear from its use. Critics, on the other hand, worry that the use of FDS might have grave implications for one’s right to keep their DNA private from government intrusion. Overall, the public remains quite divided on the issue. A study published by the Pew Research Center on February 4, 2020 showed that 48% of adults thought it acceptable for DNA testing companies to share genetic data with law enforcement, 33% thought it unacceptable, and 18% were unsure.

As of now, the legislative response to such concerns has been varied. States such as California, Colorado, Texas, and Virginia have procedures that limit the use of FDS unless all other leads have been exhausted. And, in early 2021, Maryland became the first state to require judicial oversight for the use FDS and limited its use to cases involving certain serious offenses such as murder, rape, and threats to national security. However, many states have yet to introduce any legislation which specifically addresses law enforcement use of FDS.

FDS still remains a relatively new investigative tool for law enforcement, but as its use becomes even more commonplace state and federal legislators will likely need to define the boundaries of its use. Until then, we can only speculate as to where the lines will be drawn.

* Josiah Himmelman is an Associate Editor on the Michigan Technology Law Review.

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