Detectives hunting the Golden State Killer used information from genealogy websites that led them to wrongly identify an elderly nursing home patient as a suspect in the case.
An Oregon police officer working at the request of California investigators persuaded a judge to order a 73-year-old man to provide a DNA sample in March 2017, according to newly-released court records.
The man was identified as a suspect after authorities found a rare genetic marker in 30-year-old samples of the killer’s DNA, before searches of a genealogy website led them to one of his relatives.
His daughter said police did not notify her before swabbing her ailing father for DNA from his bed at an Oregon City nursing home.
She did however go on to help investigators eliminate people who could have conceivably been the killer once she understood the situation.
The case of mistaken identity has come to light after the use of DNA data on an ancestry website led to the arrest of former police officer Joseph James DeAngelo outside his house outside Sacramento.
The 72-year-old is accused of being the sadistic attacker who killed 13 people and raped at least 50 women in California between 1974 and 1986.
Handcuffed to a wheelchair, Mr DeAngelo made his first court appearance on Friday after being charged with eight counts of murder.
Appearing dazed, he spoke in a faint voice to acknowledge he was represented by a public defender without entering a plea.
"We have the law to suggest that he is innocent until he's proven guilty and that's what I'm going to ask everyone to remember," Mr DeAngelo's public defender Diane Howard said outside court.
"I feel like he's been tried in the press already."
Investigators were able to make the arrest this week after matching crime-scene DNA with genetic material stored in an online database by a distant relative.
They relied on a website named GEDmatch, a different genealogy service to the once used in the Oregon search and did not seek a warrant for Mr DeAngelo's DNA.
Instead, they waited for him discard items and then swabbed the objects for genetic material, which proved a conclusive match to evidence that had been preserved more than three decades.
Curtis Rogers, co-founder of GEDmatch, said its data had been used without the company’s permission, expressing concern over law enforcement’s use of the site.
DNA was in the infancy of its use as an investigative tool in the mid-1980s when the Golden State Killer, also known as the East Area Rapist, carried out his final murder.
Experts believe as a police officer, Mr DeAngelo would have been aware the of new technique.
Wendell Phillips, a former Sacramento deputy who worked on the case, said police at the time suspected they were chasing either a fellow law enforcement officer or a member of the armed forces due to the methodical and meticulous nature of the crimes.
He revealed officers assigned to the task force were required to submit saliva samples to exclude anyone who shared a genetic trait identified in the attacker’s saliva found in around 15 per cent of the population.
"Obviously, you didn't want the East Area Rapist on the team," Mr Phillips said, "That turned out to be a pretty good concern."
Additional reporting by AP
Join our commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies