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"A lot of people don't realize that when you do ancestry.com or 23 and me or any of the sites where you're checking your genealogy you're uploading your life to an open source database," said San Francisco Public Defender Jeff Adachi. "Anybody can get a hold of your genetic markers and that's what's happened in this case."
The genealogy website itself states they had no idea their database was tapped by authorities.
An Oregon police officer working at the request of California investigators persuaded a judge in March 2017 to order a 73-year-old man in a nursing home to provide a DNA sample.
The Oregon City man is in declining health and was unable to answer questions Friday about the case.
RELATED: DNA linked Golden State Killer to murder of Fresno couple
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His daughter said authorities never notified her before swabbing her father for DNA in his bed a rehabilitation center, but once they told her afterward she understood and worked with them to eliminate people who conceivably could be the killer.
The case of mistaken identity was discovered as authorities hailed a novel use of DNA technology that led this week to the arrest of former police officer Joseph DeAngelo at his house outside Sacramento on murder charges. Critics of the investigative approach, however, warned it could jeopardize privacy rights.
DeAngelo is suspected of being the sadistic attacker who killed 13 people and raped nearly 50 women during the 1970s and '80s.
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The Associated Press contributed to this report.