Plane hijack MYSTERY: Fresh leads in 45-year-old case of 'plane hijacker' DB Cooper

America’s most experienced investigators have so far been unable to solve the baffling puzzle of the DB Cooper plane hijacking. In fact in June last year the FBI closed the case, taking the plane hijacker off the Most Wanted List after 45 years.

It’s one of the greatest unsolved mysteries in the history of America.

But a new clue analysed by armchair investigators could provide the missing piece of the puzzle.

Three scientists part of an investigation group called Citizen Sleuths believe a necktie left behind by DB Cooper could provide crucial information to solving the case once and for all.

DB Cooper is the pseudonym given to the man who hijacked a flight in America in 1971 before disappearing without a trace.

The smartly dressed man wore a business suit as he boarded the Northwest Orient Airlines flight in Portland, Oregon, on November 24 that year.

He was aged in his 40s and donned dark sunglasses as he ordered a bourbon then lit up a cigarette.

Soon after the plane took off for its destination of Seattle, Cooper handed a note to Florence Schaffner.

The 23-year-old flight attendant read that the plane she was travelling on was being hijacked.

Using the threat of a bomb in his suitcase, Cooper had written demands for $200,000 in cash (£132,000), which would have an approximate value of £970,560 today.

His other requests included four parachutes when they landed in Seattle, a fuel truck on standby at the airport and a second flight after that to Mexico City.

The FBI was waiting to provide Cooper with his demands as the plane touched down.

All 36 passengers were allowed to disembark but the pilot was ordered to fly Cooper to Mexico.

The hijacker wouldn’t let the pilot fly him higher than 10,000ft, and when the plane neared Nevada for a fuel pitstop, Cooper opened the rear door and parachuted out.

While no body has never been found, in 1980 an eight-year-old boy uncovered cash that matched the serial numbers of some of Cooper’s ransom money in Washington.

There have been many conspiracy theories about the whereabouts of the plane hijacker over the last 45 years, but this new necktie analysis could prove to be the missing link.

Since the FBI investigation was shut down last year, the Citizen Sleuths have continued to work tirelessly to solve the mystery.

They claim certain rare earth elements found on the JC Penney clip-on tie - which was left behind in Cooper’s 18E seat - help narrow down where he worked.

The discovery of a particular type of titanium has led the investigators to believe Cooper worked for Boeing.

Lead researcher Tom Kaye told Seattle’s King 5 News. “He was either an engineer or a manager in one of the plants.”

They have now put a callout to the public to help track down the possible Boeing employee from that era.

The researchers said: “We’re trying to solve one of the greatest unsolved mysteries of our time. And we need your help.”