This undated artist' sketch shows the skyjacker known as D.B. Cooper from recollections of the passengers and crew of a Northwest Airlines jet he hijacked between Portland and Seattle on Thanksgiving eve in 1971. The FBI says it's no longer actively investigating the unsolved mystery of D.B. Cooper. The bureau announced it's "exhaustively reviewed all credible leads" during its 45-year investigation. (AP-Photo, file)
Looking back at the D.B. Cooper manhunt (2011)
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The D.B. Cooper manhunt has been one of the longest investigations in FBI history

In order to solve a case, the FBI must prove culpability beyond a reasonable doubt

CNN  — 

The last time anyone saw D.B. Cooper, he parachuted out of a Mexico City-bound airplane with $200,000 in ransom strapped to his body, vanishing over the Pacific Northwest and initiating one of America’s greatest manhunts.

Forty-five years later, the FBI is closing the books on this unsolved case.

“We have arrived at our conclusion today that it was just time to close the case because there isn’t anything new out there,” said Special Agent in Charge Frank Montoya, Jr. “There’s a lot that goes into that decision but really it was just time.”

The infamous hijacking that took place in 1971 became one of the bureau’s “longest and most exhaustive investigations,” the FBI said.

While the bureau has chased down an immense number of leads and tips from the public, including accounts of sudden unexplained wealth and detailed descriptions matching the hijacker, none has resulted in definitive answers.

“Unfortunately, none of the well-meaning tips or applications of new investigative technology have yielded the necessary proof,” the FBI said. “Every time the FBI assesses additional tips … investigative resources and manpower are diverted from programs that more urgently need attention.”

Montoya told reporters at a news conference that the decision to close the case was his.

FBI Special Agent Curtis Eng, who told reporters he’s been on the case since 2010, said he’s fine with the decision – and a bit relieved, as new tips have the potential to take him away from other cases.

“If it [a new lead] comes in, we’ve got to follow up with it,” Eng said. “It takes time and resources away from my other cases, where there are victims now. Where there’s problems and crimes now.”

The elusive case of D.B. Cooper

On November 24, 1971, a dark-haired man who called himself Dan Cooper approached the ticket counter of Northwest Orient Airlines in Portland, Oregon, and used cash to buy a one-way ticket to Seattle.

“Cooper was a quiet man who appeared to be in his mid-40s, wearing a business suit with a black tie and white shirt,” the FBI said in a summary of the case on its website. “He ordered a drink – bourbon and soda – while the flight was waiting to take off.”

After takeoff, he handed a flight attendant a note saying he had a bomb in his briefcase, opening it to show a mass of wires and red sticks, the FBI said.

When the flight landed in Seattle, the hijacker exchanged the flight’s 36 passengers for $200,000 in cash and four parachutes, the FBI said, keeping several crew members on board. The flight took off again after he ordered it to fly to Mexico City.

At an altitude of about 1.9 miles, Cooper made his dramatic exodus, disappearing into the night from the back of the jetliner, wearing a suit jacket and with the money strapped to his body.

“If something were to arise – principally the parachutes or the money – you know, we would reopen, we would look into this, we would do what we could to bring the perpetrator to justice. But at the same time, after 45 years we just don’t think that that’s likely,” Montoya said.

The game of Clue

For years after the great escape, law enforcement and amateur investigators alike have chased theories regarding Cooper’s true identity and his whereabouts.

Whether “D.B.” – a name created by the press, according to the FBI – survived the 10,000 foot plunge into the wilderness has never been confirmed, and his true identity has never been determined.

The evidence collected over the years will now be preserved for historical purposes at the bureau’s headquarters in Washington, D.C., the FBI said.

One clue came in 1980, when a boy found a rotting package of $5,800 in $20 bills that matched the serial numbers of the ransom money.

Pieces of parachute debris and Cooper’s black tie, which he took off before jumping out of the aircraft, are also among the physical evidence being retained.

The FBI has identified more than 100 persons of interest since the case started, Eng said.

While the bureau is no longer actively investigating Cooper’s case, the saga that generated immense public interest will be sure to live on.

“We would love to have solved this, there’s no question about it. To see justice served. And it doesn’t feel good to acknowledge that this is the only unsolved skyjacking in American history,” Montoya said. “But that happens sometimes – either we’re not able to solve it or much time passes before it can be resolved.”

“There are a lot of mysteries out there,” he said, “and this is going to be one of those.”

CNN’s Joshua Berlinger contributed to this report