Bungling cops targeted the wrong man in the 'Golden State Killer' case, it has been revealed.
It has emerged that using a free genealogy site they ordered an innocent sickly 73-year-old to give DNA to clear himself.
And to make matters worse his daughter then helped detectives to nail the 'real killer' in the shocking case.
After the mistake a judge ordered her ailing father to undergo a test to prove he was not the serial murderer and rapist.
Cops used a genetic profile based on DNA from crime scenes and compared it to 189,000 others uploaded by family tree enthusiasts on free site YSearch.org.
They then used the tests to track down the care home resident, who also shared a rare genetic marker with the killer.
Armed with their court order they then took a DNA sample from the man while he was lying in bed seriously ill.
Astonishingly, his daughter was not informed about the test but after she found out she used her online family tree to help cops find people who also had similar DNA to the killer so they could be eliminated from the investigation.
The man's daughter spoke on condition of anonymity because she did not want the family's name publicly linked to the case.
Eventually, police used the same technique on a different genealogy website to track down former police officer, Joseph DeAngelo, who has now been charged with eight counts of murder.
The 72-year-old stands accused of murdering 13 people and raping nearly 50 during the 1970s and 1980s.
He made his first court appearance on Friday while handcuffed to a wheelchair but did not enter a plea.
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