Story highlights 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.

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