A construction worker found a knife buried at OJ Simpson’s California estate, but the cop he turned it over to framed it and kept it as a sick souvenir for years, according to a new report.

Los Angeles police only recently learned about the weapon when the cop asked about the records number for the Simpson murder case — so he could engrave it on the knife’s frame, TMZ reported.

It’s unclear exactly when the worker found the knife, but sources told the website it was uncovered anywhere from 1998, when the mansion was demolished, to just a few years ago. Officials are now testing it for DNA and other evidence in a top-secret investigation.

VINCE BUCCI/AFP/GETTY IMAGES

O.J. Simpson looks at a new pair of Aris extra-large gloves which the prosecutors had him put on for the jury in June 1995 during his double murder trial in Los Angeles.

The worker uncovered the weapon while digging at the site of Simpson’s Brentwood manor. As he carried it away from the grounds, he spotted an off-duty traffic cop, who was working security at a movie shoot across the street.

UNCREDITED/ASSOCIATED PRESS

O.J. Simpson’s ex-wife Nicole Brown Simpson (l.) and her friend Ron Goldman were found dead in Los Angeles on June 12, 1994.

But instead of taking the possible piece of evidence to the precinct, he allegedly took it home as a keepsake. It stayed in his house for years, sources told TMZ.

Recently, the cop, who had since retired, asked one of his buddies from the force to look up the records number for the 1994 murder of Simpson’s ex-wife, Nicole Brown Simpson. He wanted to engrave the number on a frame for the secret relic, he allegedly told his cop friend.

The officer told his supervisors, who demanded the returned cop fork over the knife.

JULIE JACOBSON/AP

O.J. Simpson listens during an evidentiary hearing in Clark County District Court, Thursday, May 16, 2013 in Las Vegas.

Police launched a top-secret investigation into the new piece of evidence, and detectives will test it for hair, fingerprints and DNA.