A newly uncovered knife is being tested for DNA, we get new insight from a top forensic investigator, and O.J. Simpson's former co-star talks about what O.J. learned about knives while training for the show.

The knife is the one key piece of evidence the Los Angeles Police Department never found in the 1994 murders of Nicole Brown Simpson and Ron Goldman.

LAPD officials confirmed on March 4 that the department was investigating a knife allegedly found buried on the Brentwood property once owned by O.J. Simpson, who was acquitted two decades ago of the murders of his ex-wife and her friend.

"It has been submitted to our lab," said LAPD Captain Andrew Neiman. "They are going to study it and examine it for all forensics, including serology and DNA and hair samples."

A construction worker demolishing Simpson's mansion in 1998 allegedly found a 5-inch Buck knife. Five years after the demolition, he allegedly gave it to a now retired LAPD traffic officer who kept it all these years as a souvenir.

Everyone wants to know: Could it be the murder weapon?

"I don't know if this whole story is bogus from the get-go," said Neiman.

"I know what happened to the murder weapon," said retired LAPD Detective Tom Lange. "We have a witness at LAX [Los Angeles International Airport] who saw Simpson exit the limo and he emptied out a small moon-shaped travel bag in a trash container right next to the entrance to American Airlines. We find out that the trash is collected three times a day, goes to one of two city dump-area landfills so that the possibility of finding that would be impossible."

Does O.J. agree? The knife revelation reportedly elicited laughs from his cell.

Simpson allegedly told a prison "snitch," who leaked his comments to the Daily Mail:

"It's complete --------. I'm not that stupid ... I got on a plane that night going to Chicago, that's all I'm gonna say," Simpson allegedly says.

A retired prison guard told the New York Post that O.J. allegedly has a saying: "If the knife is rusted, I can't be busted."

Could important clues be hidden in a long-ago shelved TV show? Did Simpson learn how to stab, stalk and secretly ambush during training for a show that never aired called "Frogmen"?

"We learned multiple ways to kill people, and it involved cutting people's throats," said actor Todd Allen.

Todd Allen is an actor and producer who worked with O.J. on "Frogmen," an action show about former Navy SEALs on special assignments.

"Everyone was convinced that the murder weapon was one of the prop knives, and there was a scene where we come in and we think that somebody has broken into our headquarters, and O.J. ends up with a knife to somebody's throat, and it turns out it is his estranged daughter," said Allen.

They filmed the pilot in Puerto Rico just weeks before the double murders in Brentwood. Allen says during training he and O.J. learned how to kill four people at once using a serrated dive knife.

The L.A. County Coroner said Nicole Brown Simpson and Ron Goldman were killed with slashes to the throat. And then the fatal wounds were multiple stab wounds to the body.

The prosecution painted O.J. as an abuser who beat Nicole.

Allen claims O.J. was obsessed with his ex-wife and Ron Goldman.

"It would come up all the time and there were a few times where he tell me stuff like 'I saw Ron Goldman driving my freaking Ferrari,' and I could tell that irritated him," said Allen.

Wally Crowder was the stunt coordinator on "Frogmen."

He wondered if O.J. did do it. Could he have used one of the knives from "Frogmen"?

"I remember hearing on the radio, and they said the knife was five and a half to seven inches with a serrated blade and I thought to myself 'Wow, that could have been the dive knife,' so I went home and measured it and I Xeroxed it and sent it to the D.A.'s office and they were like, 'Well that's circumstantial evidence we couldn't use it anyway.'"

Finding the actual murder weapon has dogged the LAPD since day one.

"He had no time to dump the knife at Rockingham," said Tom Lange.

Remember: The knife was found at the Simpson's Rockingham Avenue estate some 18 years ago.

"Given the length of time, it's really unlikely they're going to be able to recover any evidence from this knife," said forensic pathologist Dr. Judy Melinek.

Forensic pathologist Dr. Judy Melinek, co-author of Working Stiff, explains why it might be impossible for the police CSI team to determine whether the knife is the murder weapon.

Using three knives of different types and lengths, she stabs a spaghetti squash to demonstrate.

"The rind is somewhat similar to human skin, and if you take these three very different knives and stab it, it's very easy to make identical marks with knives that have very different characteristics," said Melinek. "That's why matching a knife wound is very difficult. You have to have the knife at the scene and need to be able to match it with other characteristics, such as the blood on the knife."

Testing on the knife found at O.J.'s Rockingham estate should be completed within the next week or two. But police are skeptical, saying it's not likely to be connected to the murders.

For now, Simpson is still in his cell in Lovelock, Nevada where he's serving a nine-to-33-year sentence for a robbery and kidnap conviction in Las Vegas.

O.J. Simpson up for parole next year and is reportedly worried news stories about the knife could persuade the parole board to keep him locked up.