In 1983, Rolling Stone magazine published an article recounting how New Orleans Assistant District Attorney Edward Gillin had been visited unexpectedly in 1963 by a young man who told him about a wondrous drug called LSD, which he believed would change the course of human civilization. The young man asked Gillin if the drug was legal, and whether he could import it from overseas. Gillin was puzzled and concluded that the young man was crazy. A few months later, when Gillin saw Lee Harvey Oswald on TV news reports about JFK's assassination, he realized that was the young man who had talked to him about LSD.
The article went on to lay out a speculative scenario. While Oswald was serving as a Marine Corps radar operator in Atsugi, Japan, he was recruited by the CIA to go to the Soviet Union as a fake defector in a "deep cover" operation. He was then given LSD as part of his training, by researchers who were studying whether it had value as a "truth serum" drug, and feared that the Soviets might already be using it for interrogations or to brainwash subjects. But after the CIA and JFK had a falling out over the Bay of Pigs and his policy of détente with the Soviet Union, Oswald was reactivated as a "Manchurian Candidate" to off the uncooperative president [source: Lee, Ranftel, and Cohen].
Granted, that probably sounds farfetched, unless you happen to be tripping on LSD when you read it, in which case it's utterly cosmic.