Two decades after O.J. Simpson was acquitted of murdering his former wife and her friend with a knife, police have learned of a knife reportedly found on the grounds of his former home, and kept since the late 1990s by a retired police officer. The knife is being tested for DNA evidence, police officials said Friday.

The retired officer has told investigators that while he was off-duty but in uniform, working security for a movie shoot nearby, “an individual who claimed to be a construction worker provided him with this knife, claiming that it was found on the property,” Capt. Andrew Neiman of the Los Angeles Police Department said at a news conference.

“We still don’t know if that’s an accurate account,” he cautioned. He declined to be specific about the date, but said it was “possibly during the demolition” of the house Simpson had lived in, in the wealthy Brentwood area of Los Angeles, which took place in 1998.

“It has been submitted to our lab,” Neiman said. “They are going to study it and examine it for all forensics, including serology and DNA and hair samples, and that is ongoing as we speak.”

Nicole Brown Simpson and Ronald L. Goldman were slashed to death in June 1994, outside her condominium, a short drive away from Simpson’s home, but the weapon was never found. A jury acquitted Simpson in October 1995, after one of the most widely watched and closely scrutinized trials in U.S. history.

Under the rule against double jeopardy, Simpson, a former football star and actor, cannot be tried again for the crime, no matter what new evidence is found. But news of the knife comes at a time

when interest in the case has already been rekindled by the mini-series “The People v. O.J. Simpson,” which is running on the FX channel.

And it adds new embarrassment to a police department whose reputation was battered by the case in the 1990s, amid allegations of mishandled evidence, and racism on the part of a detective central to the investigation.

The discovery calls into question how well the police searched the property. And Neiman, himself, said “I was quite shocked” that a police officer would have held onto possible evidence in a criminal case for years.

“I would think that an LAPD officer, if this story is accurate as we were told, would know that any time you come into contact with evidence you should and shall turn it over to investigators,” he said.

He was not sure whether the officer was retired at the time he received the knife. He declined to name the officer, and said the department did not know the name of the construction worker.

“If you’re seeing this story, and you believe you’re the individual that provided this knife, we’d love to have you contact the Robbery-Homicide Division,” Neiman said.

The department first became aware of the knife’s existence in the last month, Neiman said, but he would not elaborate. He also declined to say anything about the weapon, explaining that “the investigators have asked that we not be very descriptive about the knife.”

After the criminal trial, the victims’ families sued Simpson, and a civil jury found him liable for their deaths.

In 2008, Simpson, a Pro Football Hall of Famer, was sentenced to at least nine years in a Nevada prison stemming from an episode in which he stole a trove of sports memorabilia worth thousands of dollars from two dealers in collectibles.