JFK and the Alien Cover-Up

Was JFK killed because of his interest in aliens? Secret memo shows president demanded UFO files 10 days before death:

An uncovered letter written by John F Kennedy to the head of the CIA shows that the president demanded to be shown highly confidential documents about UFOs 10 days before his assassination.
The secret memo is one of two letters written by JFK asking for information about the paranormal on November 12 1963, which have been released by the CIA for the first time.
Author William Lester said the CIA released the documents to him under the Freedom of Information Act after he made a request while researching his new book 'A Celebration of Freedom: JFK and the New Frontier.'

I had heard similar stories before, but the letters are quite remarkable, assuming they are legit.