Until 1972, the Boeing 727 airliner had a curious feature - a built-in boarding ramp which could be extended whilst the plane was airborne. The villainous properties of this ramp were exploited in November 1971 by a man calling himself 'Dan Cooper'. On the 24th of November he hijacked a 727 going from Portland to Seattle, claiming to have a bomb hidden in his bag. Middle-aged, white, and wearing a suit and tie, he had managed to swan through what minimal security checks existed in 1971 (his bag wasn't even searched). Handing a note to the stewardess, and showing her what appeared to be explosive device hidden in his bag, he demanded $200,000 dollars in unmarked bills, and four parachutes.

After landing in Seattle, Cooper received his money and parachutes, and allowed the passengers to leave (in fact, they did not realise that the flight had been hijacked). Cooper then ordered the pilot to fly to Mexico, but en route to a refuelling stop in Reno, over the forested south-west of Washington, he jumped from the back of the plane with the money, and was never seen again. Having ordered the pilot to fly at less than 170mph at 10,000 feet, there was a good chance that he survived the drop, notwithstanding the fact that he jumped in the middle of the night, in sub-zero temperatures, in casual gear.

And that was that. In 1980 a child found $5,800 of the money on a riverbank near Vancouver, from which no firm conclusions can be drawn. The FBI are still technically investigating the crime, although, if he survived, Cooper would now be in his 70s (and who would turn him in, given that he entertained millions?). Along with Bigfoot and the Loch Ness Monster, Cooper's hijacking is one of the great unsolved - insoluble - modern mysteries.