LAPD spokesman Andrew Neiman said the knife was turned over in the last month by a retired police officer who said he obtained it from someone working on a construction site at the property.
Neiman said the knife would be tested for DNA evidence, but added it was possible that "the whole story is bogus from the get-go." Neiman declined to name the retired police officer or to say why the knife had only come to light last month.
Simpson's ex-wife and Goldman were stabbed multiple times in the neck and head but the murder weapon was never found at the time of the nine-month trial that ended in 1995 with Simpson's acquittal.
Simpson cannot be prosecuted again for the two murders because that would constitute double jeopardy.