WASHINGTON (AFP) - One of America's most baffling crimes - that of a hijacker who jumped out of an airliner with a parachute and ransom money 45 years ago - looks set to remain an enigma.

Nothing was heard from the well-dressed, middle-aged man ever again.

The FBI said Tuesday that after one of the longest, most exhaustive probes in its history, it will no longer actively investigate the case of the man who called himself Dan Cooper and became known as "DB Cooper."

The FBI said that after looking at all credible leads, enough is enough: resources spent on the Cooper case will be redirected to "focus on other investigative priorities."

The hijacker, wearing a business suit and tie, commandeered a Northwest Orient airlines Boeing 727 on Nov 24, 1971 as it flew from Portland, Oregon to Seattle, Washington.

After it landed safely, he obtained parachutes and US$200,000 in ransom money and freed 36 passengers.

The plane took off again with crew members as hostages, this time bound for Mexico. At some point, the man jumped out of the back of the plane using a parachute and clutching his money, falling through the freezing night air.

The case generated myriad tips but they went nowhere. No sign of the man was ever found.

Bundles of crumbling US$20 bills from the ransom money were however unearthed by a small boy on a sandbar in the Columbia River in 1980.

Evidence that will be preserved for historical purposes at FBI headquarters in Washington include that money, the man's black tie and a parachute, the New York Daily News reported.