D. B. Cooper is an unidentified man who hijacked a Boeing 727 aircraft in the northwest United States, in the airspace between Portland, Oregon, and Seattle, Washington, on the afternoon of Wednesday, November 24, 1971. The man purchased his airline ticket using the alias Dan Cooper but, because of a news miscommunication, became known in popular lore as "D. B. Cooper". He extorted $200,000 in ransom (equivalent to $1,240,000 in 2018) and parachuted to an uncertain fate. Despite an extensive manhunt and protracted FBI investigation, the perpetrator has never been located or identified. It remains the only unsolved case of air piracy in commercial aviation history.

Available evidence and a preponderance of expert opinion suggested from the beginning that Cooper probably did not survive his high-risk jump, but his remains were never recovered. The FBI maintained an active investigation for 45 years after the hijacking.

Numerous theories of widely varying plausibility have been proposed over the years by investigators, reporters, and amateur enthusiasts. A young boy discovered a small cache of ransom bills along the banks of the Columbia River in February 1980. The find triggered renewed interest but ultimately only deepened the mystery, and the great majority of the ransom remains unrecovered.

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