O.J. Simpson: No DNA On Buried Knife

7:21 AM PT -- The LAPD just released a statement that the lead investigator has not received any such information from the crime lab. Maybe so, but our inside sources say the tests have been done and no DNA was found.

LAPD detectives hit a dead end with the knife that was buried on O.J. Simpson's Rockingham estate ... TMZ has learned.

Sources familiar with the situation tell us, the DNA testing produced no matches. We're told the microbes in the soil degraded any DNA to the point it was impossible to get a meaningful result.

We're also told there was no hair or other sample that produced a lead.

TMZ broke the story ... a construction worker found the buck knife with a 5" blade buried on the perimeter of the property and gave it to a retired LAPD cop who was doing traffic control for a movie shoot. The cop took it home and put it in his tool box for more than a dozen years.

The LAPD has not announced the results, but we're told the investigation is over.