Here's a question from history: How does the dim-witted fiend bring down the genuine hero?

In 1968, Martin Luther King Jr. was one of the most revered people in the world. He was eloquent, beloved and brave; James Earl Ray was sullen, inarticulate and eminently unnoticeable. Each traveled the country; one to inspire, the other fueled by purposeless rage.

The story of how these lives met, and the murder that came of that meeting, is told in Hampton Sides' new book, Hellhound on His Trail: The Stalking of Martin Luther King Jr. and the International Hunt for His Assassin. Sides, whose previous books include Ghost Soldiers and Blood and Thunder, says that Ray's crime was no spontaneous act.

"While he was in prison, he talked about killing King," Sides tells NPR's Scott Simon. "At one point he talked about it being his retirement plan."

Still, it wasn't until Ray, a repeat offender with a long rap sheet that ran from armed robbery to mail fraud, escaped from prison and arrived in Los Angeles that those plans began to take form.

"Martin Luther King comes to Los Angeles and gives a series of speeches in which he's talking about this Poor People's Campaign that he is going to lead in Washington," Sides explains. "And something clearly sets Ray off, because the very next day he puts in a change of address form for Atlanta, Ga." -- the city where King was based.

The thing about that? "Ray has absolutely no connection to Atlanta," Sides says.

When Ray arrived in the Georgia capital, he had maps of where King lived and where he worked, but because King traveled so much, Ray began to rely on media reports to track his movements. After Ray followed King to a stop in Selma, Ala., it was reported that King would next be going to Memphis to lead a march.

"That gave him some time to react," Sides says. "Ray followed him, and it was reported in the newspaper that King's group was staying at the Lorraine Motel."

On April 4, 1968, Ray pointed a gun out of a bathroom window and looked through his 7-power scope at the balcony King stood on. Then he fired the shot that would set off an international manhunt -- and what, at the time, was the largest operation in the history of the FBI.

Sides says that considering how much the bureau had hounded and harassed the activist King when he was alive, it was surprising to learn about the massive scope of its investigation after his death.

"All the hundreds, even thousands, of false leads that were pursued," Sides says, "and as the days became weeks and the weeks became months, people were assuming that the FBI were just a bunch of fools. But very patiently and very quietly, they were assembling this case."

The big break came when investigators discovered a bundle of belongings Ray had discarded as he fled the crime scene.

"In that bundle was everything needed to solve the crime," Sides says. "His fastidious laundering is, in a way, what sank him."

Here's how: The bundle contained a pair of underwear with a laundry tag. The number on that tag led investigators to a manufacturer in Syracuse, N.Y., who led them to the laundromat Ray had used in Los Angeles, who provided the FBI with an address. It wasn't long before they had a photo, too, and could call in the help of both Canadian and English police.

The Royal Canadian Mounted Police used the photo to sort through passport applications and identify a Ramon George Snade who looked just like -- and in fact was -- James Earl Ray. Scotland Yard was then able to intercept Snade (aka Ray) as he boarded a plane in London.

Ray was questioned by Scotland Yard's legendary Thomas Butler, who Sides describes as a "master interrogator." But to this day, there are many questions that remain unanswered. One such question is whether Ray acted alone.

"In the book, I do leave a lot of doors ajar about what sort of level of help he might have had," Sides says.

Ray used a number of aliases when he traveled, most of them actual people living in the suburbs of Toronto; Sides argues that Ray must have had help getting those names.

Even more mysterious is how he sustained himself without any kind of financial backing while he stalked King, killed him and then fled from authorities.

"He did rob a bank in London, and he did rob a jewelry store in London," Sides acknowledges. "He wouldn't have done those things if he wasn't desperate for money. So if he had some help in terms of a conspiracy financing him, they clearly hadn't given him very much money."

Sides says the reason we still have these questions is because once authorities caught up with Ray, he never really told them the truth -- like when he claimed a man named Raul was the one who actually pulled the trigger.

Says Sides: "He went to his grave with all these secrets that unfortunately we'll probably never have the answers to."

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