James Swanson, Author of the Book Called Chasing King's Killer: The Hunt for Martin Luther King, Jr.'s Assassin

WASHINGTON, DC - DECEMBER 12: This rare, previously unpublished J. Edgar Hoover letter, in which the FBI director expresses his anger at Martin Luther King, was found by James Swanson, author of the book Chasing King's Killer: The Hunt for Martin Luther King, Jr.'s Assassin, Tuesday, December 12, 2017, in Washington, DC. Swanson says he found the letter several years ago tucked inside the pages of an old book by Hoover he found in a bookshop. The letter sheds a bit more light on the historic malice that the FBI held toward King. (photo by Jahi Chikwendiu/The Washington Post via Getty Images)