The case has puzzled FBI investigators for the last 45 years, and is the country's oldest unsolved skyjacking. "Over the years, the FBI has applied numerous new and innovative investigative techniques, as well as examined countless items at the FBI Laboratory".
Investigators from the Federal Bureau of Investigation have suspended the effort to identify the hijacker who, in 1971, parachuted from the rear air-stair of an airborne Northwest Orient Boeing 727 after securing a $200,000 ransom.
The famed police sketch showed a bespectacled man of average height, wearing a sport jacket and thin tie, fashion very much of the iconic, buttoned-up era in 1950's and 60's business.
"Although the FBI will no longer actively investigate this case, should specific physical evidence emerge ― related specifically to the parachutes or the money taken by the hijacker ― individuals with those materials are asked to contact their local FBI field office", the FBI said.
Cooper demanded $200,000 in American currency and four parachutes, which he received in exchange for allowing the passengers to leave the plane in Seattle.
Cooper was never found, fueling a host of theories about his identity and fate.
The FBI said the decision to close the case was due to the fact that, after 45 years of time, effort and money, they have no solid evidence and all leads have come up dry. Cooper kept several crew members on board and ordered them to set a course for Mexico City.
The case sparked worldwide interest and spawned movies including "The Pursuit of D.B. Cooper", starring Treat Williams as Cooper and "Bigfoot vs. D.B. Cooper", with Eric Roberts.
Cooper parachuted out of the plane, with his money, at some point between Seattle and Reno, Nevada, opening the aft stairs himself. Over the years, agents had considered 800 suspects and whittled down the list to less than two dozen. Handing a stewardess a note saying he had a bomb and flashing a suitcase full of wires, he demanded $200,000 in ransom money and parachutes.
Nine years later, a boy digging on a beach discovered three bundles of damaged $20 bills worth US$6,000 which matched the serial numbers of the cash given to Cooper.
"Evidence obtained during the course of the investigation will now be preserved for historical purposes at FBI headquarters in Washington, D.C.", the agency said.
The case is the last unsolved skyjacking, with the spectacle of Cooper's actions long holding the public's attention, Geoffrey Gray, who wrote the 2011 book "Skyjack: The Hunt for D.B. Cooper", told the AP.