He was a mentally ill man who died after eating rat poison,
dressed up to look like a British officer
During World War II, the allies deceived the Germans with a clever deception - a fake dead courier carrying a letter detailing fictional plans for an invasion of Sicily.
Each stage of the deception had to be worked out in advance. Martin’s personal effects needed to be detailed enough to suggest that he was a real person, but not so detailed as to suggest that someone was trying to make him look like a real person... Operation Mincemeat would only work if the Germans could be fooled into believing that the British had been fooled.” It was an impossibly complex scheme, dependent on all manner of unknowns and contingencies. What if whoever found the body didn’t notify the authorities? What if the authorities disposed of the matter so efficiently that the Germans never caught wind of it? What if the Germans saw through the ruse?
But that's not the most interesting part of the story. In an excellent magazine piece on deception in The New Yorker, Malcolm Gladwell asks this question: in the espionage game, when each side is constantly trying to fool the other, how can anyone ever discover the truth?
This is a problem even outside the spy business. With so many people having so many different agendas, it's difficult to discover the truth about anything. You can find this at work in deceivers of all types: con men, magicians, politicians. A deceiver can easily lead you down the wrong path, but if the deceiver knows you're suspicious, what's to prevent a deceiver from leading you down the right path and making you think it's the wrong path?
For a good comic example of this problem, watch this clip from The Princess Bride.