Catholic peace activist Jim Douglass believes in conspiracy theories, including the Big Daddy of them all-the conspiracy to kill President John F. Kennedy. “There is no mystery as to how and why and by whom he was assassinated,” said Douglass, who lives in Birmingham, Ala. And he’s not referring to Lee Harvey Oswald, who he believes was framed as the assassin by the Central Intelligence Agency. Kennedy’s enemies were covert operatives in his own government, Douglass alleges. That’s not a groundbreaking theory. Filmmaker Oliver Stone and others have covered that territory before. But in his new book, “JFK and the Unspeakable: Why He Died and Why It Matters,” from the Catholic publisher Orbis Books, Douglass offers up a religious interpretation of the assassination, with help from the late best-selling monk Thomas Merton.