Marla Cooper, the alleged niece of hijacker D.B. Cooper, said when she was 8 years old she heard her two uncles planning something suspicious while at her grandmother's house in Oregon.

A day later, Northwest Orient flight 305 was hijacked, and her uncle L.D. Cooper came home and said he was in a car accident.

"My two uncles, who I only saw at holiday time, were planning something very mischievous," she told ABC News. "I was watching them using some very expensive walkie-talkies that they had purchased. They left to supposedly go turkey hunting, and Thanksgiving morning I was waiting for them to return."

Marla believes her uncle Lynn Doyle Cooper is the one who hijacked the jetliner in 1971 and leaped from the plane in a parachute, making away with $200,000 in cash.

"I'm certain he was my uncle, Lynn Doyle Cooper. Who we called L.D. Cooper," she said.

Marla said after the crime was pulled off she heard her uncle said "we did it, our money problems are over, we hijacked an airplane."

But it is believed that much of the $200,000 was lost as D.B. Cooper crash down.

For 40 years D.B. Cooper's identity has been a mystery, leaving a suspicious cold case in the FBI's files. More than 1,000 leads have been checked since Cooper made his getaway leaped on Nov. 24, 1971 over the Pacific Northwest.

The FBI recently announced that it is following a promising new lead in the D.B. Cooper case, which was given as a tip from a retired law enforcement official.

The tip federal agents are following is that a man who died in the Pacific Northwest was Cooper 10 years ago may be the infamous D.B. Cooper. Agents have already requested the man's personal effects so that prints can be compared with those found at the hijacking scene. Agents are also working with the man's family members.

Marla told ABC News she has provided FBI agents with a guitar strap and a Christmas photograph of her uncle picture with the same strap.

Federal agents are now searching an item they got for fingerprints at their forensic laboratory in Quantico, Va. This will be checked against partial prints found from the hijacking scene.

At the same time, the FBI will hunt for proof that L.D. Cooper was on the jet in 1971.