Hampton Sides gives an unparalleled portrait of King assassin James Earl Ray and the FBI hunt for him in Hellhound on His Trail.

Why do people want to see King's murder as something grander than the work of fugitive petty criminal James Earl Ray?

Some people think that it takes a grand conspiracy to bring down a great man. Also, King's entourage and family have perpetuated the idea. And the fact that J. Edgar Hoover's FBI tried so hard to smear and ruin King before the assassination certainly helped feed conspiracy theories. But in my estimation, Ray did it. He bought the gun [that shot King], the scope, and the ammo. He checked into that flophouse [from which King was shot] two hours before the assassination and left the scene one minute after the assassination. Ray admitted every one of those things, but then said that some other guy named Raoul pulled the trigger.

In your book you refer to Ray mainly by his aliases. Why?

At first people had no idea who committed the crime—they called him “the man in 5B”—so I wanted the book to feel like a mystery. I was also interested in how Ray inhabited his aliases. He started trying on new lifestyles and looks, wearing business suits and going to dancing school. When he became Ramon Sneyd, he got glasses and tried to look dignified and professorial.

What kind of character lurked beneath those shifting personae?

Ray really did want to be somebody. In the lore of his pathologically dysfunctional family, he was supposed to be the smart one, the ambitious one. He thought he would be welcomed as a hero somewhere [for killing King]—maybe in [white supremacist] Rhodesia, maybe in Alabama. Ray was an evil man, but he was also struggling to figure out his place in the world: reading self-help books, undergoing hypnosis, going to shrinks. Maybe he could have gone clean but for that burning ambition and restlessness.

After stalking King themselves for so long, how did the FBI respond when King was shot?

Paradoxically, Hoover's well-known hatred of King made the FBI manhunt more intense. Perhaps the fear was that the bureau's eavesdropping and bugging and smearing [of King] would come out. You can see in Hoover's memos an almost desperate need to catch the assassin. So the same FBI agents who had been trying to ruin King were now trying to find his killer. I became fascinated by their old-fashioned, competent, gumshoe detective work, how the case builds slowly on the teeny little details of laundry tags and fibers and fingerprints and numbers on transistor radios. It was one of the FBI's finest hours.