The Northwest Airlines notorious skyjacking saga that has baffled authorities for 40 years may have finally been solved.

An Oregon woman who claims her uncle was the elusive criminal known only as DB Cooper says she has been told by the FBI that her evidence is enough for them to close the file on the case.

Burdened by guilt over her knowledge surrounding the case, Marla Cooper came forward earlier this year, claiming she had a 40-year-old family secret protecting her uncle, a man named Lynn Doyle Cooper.

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Is it the same man? Maria claims her uncle Lynne Doyle Cooper, left, was the infamous hijacker, right

Niece: Marla Cooper says her family's 40-year-old secret reveals that her uncle, Lynn Doyle Cooper, was the notorious skyjacker

Marla Cooper said she was eight years old when her uncle, whom she called LD Cooper, came to her home, badly injured, for Thanksgiving in 1971 - the day after the infamous incident. He claimed his injuries were the result of a car crash.

Later, she said, her parents came to believe that L.D. Cooper was the hijacker. Mrs Cooper never saw her uncle again after that day and was told he died in 1999.

It was the FBI's most promising lead for the mystery of who was behind the hijacking of Northwest Airlines flight from Portland to Seattle following a bomb threat on the night of November 24, 1971.

Imitating art: Marla Cooper says her uncle was fascinated with comic book character Dan Cooper, the same name as the one given to Northwest Airlines on that night in 1971

Marla Cooper also provided investigators with a photograph of LD and a guitar strap that he owned for fingerprint testing.

While the results of the fingerprint test have not yet been determined, authorities seem eager to end the investigation.

Miss Cooper told NBC affiliate WFIE: 'Regardless of the findings of the fingerprints, they would be closing the case after this. He said, "I am certain your uncle did it. I feel certain that your uncle did it. And that, what's the point in continuing the investigation?"'

In addition, Marla Cooper said that her uncle was fixated on a comic book character named 'Dan Cooper,' the name the skyjacker gave the airline before boarding.

FBI officials told the station that they are conducting the tests, but would not comment on their next move in the case.

As for the $200,000 ransom, she believed Lynne Cooper lost it all as he parachuted to earth.

The mysterious hijacking has intrigued everyone from federal agents to amateur sleuths.

On that day in 1971, the suspect, who was wearing a suit and sunglasses, boarded the flight after buying a $20 one-way ticket to Seattle.

Cool culprit: Impressions of Cooper as a smartly-dressed man have added to the fascination nature of the mystery

Map: Locations in Washington where Cooper was originally thought to have landed and where some of the ransom money was found in 1980

After getting on the plane, he ordered whisky and lit a cigarette before passing a flight attendant a note that read: 'I HAVE A BOMB IN MY BRIEFCASE. I WILL USE IT IF NECESSARY. I WANT YOU TO SIT NEXT TO ME. YOU ARE BING (sic) HIJACKED.'

Cooper told the captain that in return for $200,000 and four parachutes, he would allow 36 people to leave the plane when it landed in Seattle.

Vital clue: Cooper's cheap clip-on tie was one of the items recovered after the skyjack

The FBI agreed to the swap and the plane took off again under Cooper's orders to fly towards Mexico at an altitude of under 10,000 feet.

Somewhere over the lower Cascade mountains in southwestern Washington, Cooper stepped out of the plane with a parachute strapped to his back.

He was never seen again.

There were more than 1,000 possible suspects considered over the past four decades.

Several people even claimed to be Cooper at times, but were dismissed on the basis of physical descriptions, parachuting experience and, later, by DNA evidence recovered in 2001 from the cheap, clip-on tie the skyjacker left on the plane.

Items recovered from the skyjack include $5,800 of the stolen money, in tattered $20 bills and Cooper's tie.

Many believe that Cooper was Richard McCoy, a Vietnam War veteran, experienced parachutist and BYU political science student who staged a similar hijacking several months later.

Plot: A hijacked Northwest Airlines jetliner 727 sits on a runway for refuelling at Tacoma International Airport on November 25 1971