US detectives are investigating a knife purportedly found some time ago at the former home of OJ Simpson.

The former American footballer was controversially acquitted of murder charges over the 1994 stabbings of his ex-wife Nicole Brown Simpson and her friend Ron Goldman.

The knife was supposedly found by a citizen, possibly during demolition of the home years ago, and turned over to a now-retired police motorcycle officer who was working as a filming location security guard, Los Angeles Police Captain Andy Neiman said.

The knife came to light in the last month, but Mr Neiman did not say how that occurred. He stressed that the authenticity of the story was not confirmed.

"This whole story is possibly bogus from the get-go," he said.

The knife is being analysed by a Los Angeles Police Department crime lab. Mr Neiman said investigators did not know the identity of the person who handed it over and asked him or her to come forward.

The weapon used in the killings has been a mystery for decades.

The killings on June 12 1994 led to the "trial of the century" in which the former football star was acquitted in October 1995 by a jury that deliberated only four hours.

In 1997, a civil court jury found Simpson liable for the deaths and awarded millions of dollars in damages to families of the victims.

Mr Neiman did not believe that Simpson could be charged again with murder if the knife is linked to the killings, citing double jeopardy.

"I'm not an attorney, but it's my understanding from being a police officer for nearly 30 years that double jeopardy would be in place here," he said.

Simpson is imprisoned in Nevada for a 2008 kidnapping and armed robbery conviction.

The police department is looking into whether criminal charges could be filed against the ex-officer who held on to the knife, according to Mr Neiman. An officer who comes into contact with evidence is required to turn it over to investigators, he said.