His 1980s Disappearance Led Investigators To A Serial Killing Duo — Who Is Paul Cosner?

When Paul Cosner vanished in 1984, his girlfriend and family were incredibly concerned. They were right to be. The disappearance of Paul Cosner ultimately helped expose the crimes of a depraved serial-killing duo, Leonard Lake and Charles Ng.

The pair's murder spree is documented in the upcoming three-part special "Manifesto Of A Serial Killer," premiering Sunday, January 1 at 7/6c on Oxygen. Before the premiere, learn who Paul Cosner was and how his disappearance led to the capture of the two killers.

Paul Cosner grew up in Ohio, where he graduated from high school in 1963.

"Paul was two years ahead of me in school. Our last name was Cosner and so he was known as 'Big Cos', and I was 'Little Cos.' And then our dog was Cosmo," sister Sharon Sellitto told local outlet ABC6 in 2022. "And we just had the perfect life."

He attended Ohio State University before he headed out west and landed in San Francisco, California in 1969, according to The Charley Project. 

"He was very happy," Sellitto told ABC6.

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He started working as a used car dealer out there — but it was a car sale that seemingly led to his disappearance.

Cosner, then 39, vanished on November 2, 1984. He had left his home to meet with a potential buyer for a vehicle he had advertised for sale in the papers, who he had described as “weird,” according to The Charley Project.  His girlfriend said he told her he would be back by 8 that night to watch TV with her.

He never returned home.

His gold 1980 Honda Prelude disappeared along with him — but the car was finally located in 1985.

"Then they caught two men trying to shoplift in Paul's car in South San Francisco," Sellitto told ABC6.

The two men in question were friends Charles Ng and Leonard Lake. Some of Cosner’s personal effects were in the stolen car, too.

“I went down to where they had the car and demanded that they let me see it, which they did. And it had bullet holes and blood in the headrest and I knew that Paul was dead,” Sellitto said.

Ng was able to evade police, but Lake was taken into custody. They weren’t able to get much out of him, though, before he killed himself by taking a cyanide capsule he kept on himself.

But investigators had already discovered something horrifying had been happening at a remote cabin Lake rented in the foothills of the Sierra Nevada mountains. Ng and Lake had been luring people to the residence, where they killed the men and children but held women captive in a small bunker Lake had constructed on the Wilseyville cabin’s grounds. They then tortured and raped the women before they killed them. They even videotaped themselves as they committed the horrifying and brutal acts.

Ultimately, the pair murdered at least 11 people but it's thought they possibly killed as many as 25.

Your First Look at Manifesto of a Serial Killer

Ng was eventually caught in Canada and extradited to the United States, where he stood trial in 1998 on 12 counts of murder. He was convicted in 1999 on 11 counts, for the murders of six men, three women, and two baby boys from 1984 to 1985, according to the New York Post.

The charge he was not convicted on was the murder of Cosner. The family was destroyed by the news, Sellitto said.

Cosner’s body has never formally been identified.

There was a victory that came in March 2001, when John Dearborn, presiding judge of San Francisco Superior Court's probate division, officially declared that Cosner had been a homicide victim, SFGate reported at the time.

“Paul Steven Cosner went missing in San Francisco on November 2, 1984," the order said. "He has not been heard of since, and the court finds that he was the victim of murder at the hands of Leonard Lake and Charles Ng."

More recently, there has been another attempt to identify remains found on the cabin property. 

"The advancement of DNA technology has greatly increased over the years, specifically to a point where we think we're very hopeful we can return or legally find out who the victims are in the crime,"  Lt. Greg Stark of the Calaveras County Sheriff's Department said in August 2021, according to ABC10.

Sellitto confirmed she was recently asked to give another DNA sample.

"That's a very good hope and possibility that Paul's in the bones that they're testing now and I will finally get to put him next to mother and keep my word to her," Sharon said. “... I think then if we find Paul, then it's over. I can stop. It's over.”

Watch the three-part special "Manifesto Of A Serial Killer" when it premieres on Sunday, January 1 at 7/6c on Oxygen.