"It's a very unique case...Agents have been actively assigned to it and it's passed on from generation to generation...of agents that have worked leads as they have developed," said Brad Garrett, an ABC News consultant and former FBI profiler.
Garrett said the FBI is likely examining the life of Marla Cooper's uncle for more clues that he could be the infamous D.B. Cooper.
"Does this guy's background actually fit someone that could have pulled this off because this guy did have a proficiency in a 727 plane, how low it would fly, how slow it would fly and that you could jump out the back of it," Garrett said.
After he received the money in $20 bills and the parachute, he ordered the plane to take off for Mexico. Cooper then did the unthinkable when he lowered the back stairs and jumped out of a speeding 727, thousands of feet over the Pacific Northwest during a raging storm.
He disappeared, despite a massive manhunt that has become the stuff of legend and even a 1981 movie. Throughout the years many leads in the case have became dead ends, and it remains the only unsolved hijacking in U.S. history.
The case was reignited when a male suspect's name was given to the FBI by a law enforcement agent, as was a guitar strap. Sources familiar with the case confirm that it was Marla Cooper who prompted the latest flurry of investigation.
So far no fingerprints have been found on the guitar strap, and the F.B.I. will not officially comment on the case.
"My two uncles, who I only saw at holiday time, were planning something very mischievous. I was watching them using some very expensive walkie-talkies that they had purchased," she said. "They left to supposedly go turkey hunting, and Thanksgiving morning I was waiting for them to return."
A day later, Northwest Orient flight 305 was hijacked, and her uncle L.D. Cooper came home claiming to have been in a car accident.
"My uncle L.D. was wearing a white t-shirt and he was bloody and bruised and a mess, and I was horrified. I began to cry. My other uncle, who was with L.D., said Marla just shut up and go get your dad," she said.
Marla Cooper is now convinced there was not a car accident, but that her uncle was injured crashing to earth in a parachute. She says that she also remembers a discussion about the money that day.
"I heard my uncle say we did it, our money problems are over, we hijacked an airplane," she said.
It later became clear, however, that there was no money. It is believed that the hijacker lost much of the cash as he came crashing down.
Marla Cooper says that her two uncles wanted to return to search for the cash, but her father refused. She believes this was because the FBI search was just beginning to take shape.
After that Thanksgiving Day she never saw her uncle again. She was told he died in 1999.