The O.J. Simpson case took another Hollywood twist Friday — when LA cops said they were testing a bloodstained knife unearthed at his old property to see whether he used it to kill his ex-wife and her friend.

Even though the football legend remains untouchable in a court of law because of his 1995 acquittal on murder charges, authorities were looking for DNA and other biological evidence on the folding Buck knife that emerged through an implausible chain of custody.

A hardhat claims he found it while razing Simpson’s Brentwood mansion in 1998.

But the cop kept it in his home for more than a decade as a souvenir instead of turning it over to his bosses.

“I don’t know why that didn’t happen or if that’s entirely accurate or if this whole story is possibly bogus from the get-go,” LAPD Capt. Andy Neiman said on Friday.

In late January — right before the season premiere of the popular FX series “The People v. O.J. Simpson” — the now-retired cop, identified by NBC as George Maycott, contacted a friend in the homicide division and told him he was getting the knife framed to hang on his wall.

He wanted the case’s serial number to engrave on the frame.

The pal told his bosses, and the LAPD took the knife, which will be examined for evidence including hair and fingerprints at the department’s Serology/DNA Unit next week, sources told TMZ.

Cops who saw the knife said it appeared to have blood residue on it.

Sources told NBC the knife would be tested rigorously but that initial analysis showed its characteristics may be “inconsistent” with the murder weapon.

In 1994, Simpson riveted the nation with his slow-speed police chase that ended with his arrest on charges of murdering ex-wife Nicole Brown Simpson and her pal Ron Goldman.

The murder weapon was never found, and Simpson was acquitted in 1995 at the end of “the trial of the century.”

Asked about the new development, Goldman’s father, Fred, said he didn’t want to jump to conclusions.

“I’m just not saying anything, because there are too many unknowns. I’m going to wait until it plays itself out a little bit,” he said.

Neiman recalled that he was “quite shocked” to learn that the traffic cop, who he said retired in the late ’90s, had kept what may have been a murder weapon.

“I was really surprised,” Neiman said. “I would think that an LAPD officer would know that any time you come into contact with evidence, you should submit that to investigators.”

He cannot face departmental discipline because he is retired. But authorities did not rule out criminal charges against the officer for withholding the potential evidence in a criminal case.

Simpson, an NFL Hall of Famer and Heisman Trophy winner, was convicted in 2008 of committing an armed memorabilia heist at a Las Vegas hotel-casino. He is up for parole in October 2017.

Although he beat the criminal charges in the murders, a civil jury found him liable for the deaths and awarded millions of dollars to the victims’ families.

With Post Wire Services