A knife reportedly found at OJ Simpson's former estate is probably not connected to the killings of his ex-wife and her friend, a law enforcement source has said, but it will take at least three weeks to know for sure.

Investigators are examining the knife for DNA or other material that could possibly link the weapon to the 1994 murders. Results were not expected for at least three weeks, Captain Andy Neiman said.

Meanwhile, a law enforcement official with knowledge of the investigation said detectives doubt the knife is connected to the killings.

The source said the knife was commonly used among gardeners and was too small to make the wounds that killed Nicole Brown Simpson and Ronald Goldman.

Both Ms Simpson and Mr Goldman had deep gashes to their necks, in addition to a number of other extensive knife wounds.

The weapon used in the killings has been a mystery for decades. Other knives have surfaced during the case, but they were not linked to the crimes.

On Friday, Los Angeles police revealed that they were examining a knife reportedly found at Simpson's estate years ago.

Police said a building worker gave the knife to an officer working as a security guard at a filming location. The officer then kept the knife for a number of years, police said.

Trent Copeland, a lawyer who represents the officer, said his client retired in 1998 and that the builder gave him the knife in 2002 or 2003, well after a jury found former football star and actor Simpson not guilty of the murders.

Mr Copeland said the officer, George Maycott, immediately called police to report the knife.

"Someone put him on hold, that person came back several minutes later, said he spoke to a supervisor who said, 'Double jeopardy is attached to this case, OJ's been acquitted. If that knife had blood on it there's really nothing we can do about it, so we don't want anything to do with this'," he said.

Mr Maycott then kept the knife in a toolbox for the next 13 years or so.

"He was not this sort of bumbling Keystone Cop who cavalierly decided he would take what could have been a pivotal piece of evidence and put it in his bag," Mr Copeland said.

"He knows that he did exactly what any diligent professional officer would have done and that is you call LAPD immediately - and that's what he did."

The bodies of Ms Simpson and Mr Goldman were found with multiple stab wounds outside her home on June 12 1994.

The discovery led to the so-called "Trial of the Century", in which Simpson was represented by a team of high-profile lawyers led by the flamboyant Johnnie Cochran. A jury acquitted Simpson in 1995 after deliberating for only four hours.

In 1997, a civil court jury found him liable for the killings and awarded 33.5 million dollars in damages to the victims' families.

Simpson, now 68, who has always maintained his innocence, is serving a sentence of nine to 33 years in a Nevada prison for a 2007 armed robbery and kidnapping conviction in which he tried to retrieve football memorabilia. He is eligible for parole next year.