For my book, I spoke to the surviving members of the commission's staff and then pursued the leads they hadn't been able to follow - because Warren resisted or because, it is now clear, evidence had been hidden from them. I was never swayed by the theories of a mob plot, if only because it seemed so unlikely that the Mafia would enlist such pathetic misfits as Oswald and Ruby in the crime of the century. I was much more intrigued by evidence - denied to the commission's staff - suggesting that Oswald had talked openly about his plans to kill the president and that he may have been promised help if he were ever able to succeed. Much of that evidence involves his mysterious visit to Mexico City several weeks before the assassination, when Oswald, a self-proclaimed Marxist, was apparently trying to get a visa to defect to Cuba.