DNA has many uses, some malign, some medically worthy. But there’s a particularly splendid case. It led to the arrest of California’s suspected Golden State Killer last week after a manhunt that spanned decades.

Joseph James DeAngelo, the 72-year-old ex-cop alleged to have sadistically killed at least 12 men and women, raped at least 100 girls and women and burglarized up to 130 homes for rape practice and research, had largely been forgotten. California has many monsters.

If the killer’s crimes began around 1976 and his last murder was indeed in 1986 — when he bludgeoned Janelle Cruz’s head so ferociously that her teeth landed in her hair — he stopped for a reason. Some assume he aged out but, as we learn from the Charlie Roses and Bill Cosbys of this world, humans keep doing the things they enjoy. Everyone has a hobby.

The Golden State Killer liked to sneak into couples’ bedrooms, blind them with flashlights, make the woman blindfold and tie up the man, place dishes on the man’s back and say if they rattled, he’d kill both of them.

He would tell a raped woman not to move. An hour would pass. She’d think he was gone, try to escape, and suddenly the knife was at her throat again. Paul Bernardo began his career doing this to his rape victims in Scarborough.

Sacramento women were raped while their husbands listened helplessly in another room, while toddlers played beside the bed. At a public meeting about the rapes, a local man blamed men for not fighting back as their wives were raped, as a good husband would do. A week later, he and his wife were attacked. The police believe the killer attended the meeting and chose his victims there.

He chose to kill very beautiful women, the kind that online violent “involuntarily celibate” losers are said to claim as their due, most recently in Toronto. He left entire cities throughout California paralyzed with fear for years.

But one investigator believes that in the ’80s, the killer realized the world was changing. DNA profiling had been invented and was fast improving, along with geographic profiling (led by Canada’s Kim Rossmo). Cold cases were being reopened, this time with hope.

A dancer at the strip club DeAngelo frequently visited said he told her recently, “‘They'll never get my DNA.’ He said his sister had taken one of those tests. He got all sweaty and stuttery.”

A DNA match ties a former police officer to some of the crimes committed by a California serial killer behind at least 12 homicides and 45 rapes throughout the state in the 1970s and '80s, police officials announced April 25. (The Associated Press)

DeAngelo worked as a cop during the era of the Visalia Ransacker, a long chain of weird break-ins. Like Canada’s serial killer/rapist/fetishist Col. Russell Williams, the GSK stole females’ underwear and posed it about the house, always knew where the lubricant was (he preferred Vaseline Intensive Care Lotion), left sinister messages, and was adept at entry and escape.

In 1979, DeAngelo was fired for having shoplifted dog repellent and a hammer, of all things. The cops had wondered how the DSK managed to keep dogs away as he crawled around women’s lawns and fences.

Stories like these are woven into women’s lives. We take precautions, install deadbolts, blinds and motion sensor lights, bring flats to run in, watch our drinks, are cautious about repairmen. It’s a fire safety drill, but only for women. Many men know nothing of this because they don’t have to.

Police use of DNA has been a particular gift to female victims of crime. Previously, a rapist would wear gloves. Now that might not help. Before DNA, the only physical information the police had on the GSK was his height, his habits, his Robert Durst-like muttering, and, something the victims agreed on, a notably small penis. It was short and narrow.

The American media reaction last week was all about publicly posted DNA on open sites being used by the police to arrest DeAngelo. How they fretted. Was this not Dystopian, intrusive, a case of police overreach that would lead to mass DNA mapping, like China’s fiendishly good facial recognition technology?

Perhaps, perhaps not. Gizmodo reports that the police mainly used GEDmatch, an open source site that anyone can use, generally to research family histories. They also got a subpoena for Family Tree DNA to give up a name for DNA found on ysearch. I say this is a fair use of DNA.

The media reaction showed that victims don’t rate. They’re old news. Tech is fun, digital privacy is the story of the moment — that was the tenor of the coverage of DeAngelo, alleged suburban monster and father of three daughters.

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Think of journalist Michelle McNamara, whose 2018 book, I’ll Be Gone in the Dark, kept the hunt for the killer in the public eye. She died before publishing it, having wrecked her own health with overwork.

Americans who were not raped by this man might well wish to help the police assist those who were. If you gave away your privacy to Facebook for fun, you might find this a more noble cause.

Only DNA could have found him. Studied accurately, it protects everyone except people like the Golden State Killer, who in 2001 phoned a 1977 victim and whispered, “Remember when we played?”

Heather Mallick is a columnist based in Toronto covering current affairs. Follow her on Twitter: @HeatherMallick