Civil rights leader Martin Luther King was assassinated in Memphis, Tennessee, 40 years ago on 4 April 1968.
A year later, James Earl Ray admitted to being the assassin. Because of that guilty plea there was no full trial. But Ray changed his story almost at once and until his death in prison in 1998 insisted he did not murder Dr King. So was he the killer? And if so, did he work alone?
Martin Luther King was shot on the balcony of the Lorraine Motel
To many, 40 years after his death, Martin Luther King has become a sort of secular saint.
In 1968, many whites in Tennessee saw things differently. He was a rabble-rouser, an agitator, possibly a Communist.
In a society built on open racial divisions, his arrival in Memphis in support of striking black sanitation workers was a source of white anger and resentment.
In that very different America, not everyone was saddened by his death.
Dr King died of a bullet wound to the throat just after 6pm on 4 April. He had been standing on the balcony of the Lorraine Motel, talking to colleagues in the motel parking lot about dinner plans.
Among them, aged 26, was Jesse Jackson - later a candidate for the presidency. At this distance, he can smile with affection recalling Dr King's last words.
"I was coming across the parking lot and he said 'Jesse - you don't have on a tie'. I said the prerequisite for eating was an appetite, not a tie! He said I was crazy and laughed.
"Then he looked at the guy who was with me, (the musician) Ben Branch, and he said 'Ben be sure to play my favourite song tonight - Precious Lord'. And then the bullet hit him in the neck and he was killed instantly."
The official version would later be that James Earl Ray, working alone, had shot Dr King with a rifle from the small bathroom at the rear of the run-down boarding house across the street from the motel.
James Earl Ray confessed to the murder but then changed his story
Jesse Jackson believes that is a partial truth, at best.
"I'm convinced Ray was not the lone shooter. He didn't have the money, the mobility nor the motive to have done it. The fact that James Earl Ray was able to get out of the city and out of the country means he was a hired hand. The government seems to have had the most motive for attacking Dr King."
The official line, never tested in court, remains that Ray was solely responsible for the murder - and initially Ray admitted to that.
He had been a no-account criminal, brought up in poverty in Missouri, who escaped from jail a year before the murder. After the assassination he fled Memphis, escaping to Canada and then London.
He travelled briefly to Lisbon, apparently hoping to arrange contacts with white mercenaries in Africa. He returned to London and was finally arrested at Heathrow trying to board a flight for Brussels.
Those are some of the few incontrovertible facts. A small library of books exists about what may have happened between Ray's jailbreak and his arrest.
Those who insist Ray was indeed the gunman face difficult questions - yet so do those who claim he was not.
There are many such questions. Here are three of the most obvious which each side faces; first, those which his defenders have to answer:
Ray at first admitted to the murder. Isn't that the end of the story?
Author and lawyer William Pepper, now writing his third book about the case, says Ray was poorly advised by his first attorney, the late Percy Foreman. Mr Foreman told his client that unless he pleaded guilty he could face the electric chair (although the state of Tennessee carried out no executions between 1960 and 2000). Ray sought to change his plea within days but was not allowed to do so.
If Ray was innocent, why flee Memphis at all?
Ray always maintained he heard on his car radio that Memphis police were looking for someone resembling him following the assassination. As an escaped convict he could not afford to give himself up.
No one denies Ray bought a gun at least similar to that used in the shooting shortly beforehand. Why did he do so? And why rent a room in the boarding house opposite the Lorraine Motel?
This all touches on Ray's basic defence. He claimed that while on the run he met a man called "Raoul" in Canada who set him up as a patsy. Raoul, claimed Ray, said he wanted him to run guns. The rifle was a sample for potential buyers and the room was rented - using an assumed name - as a potential meeting place. Pepper claims Raoul is alive today and living near New York City. Others have doubted his very existence, suggesting he was invented by Ray to explain away all awkward facts.
On the other side, there are three key points which those who argue Ray was the gunman have to answer:
The shot which killed Martin Luther King was highly accurate. Yet Ray, by no means a marksman, is said to have shot at an awkward angle through a half-closed window while standing in a bath-tub.
The author Gerald Posner wrote a book explaining why Ray must be the murderer. Posner says other writers overstate the difficulty of the shot and that Ray had used guns in petty robberies. Ray's lack of gun-skills also raises problems for those who say he may have been the gunman but was employed by others. With so many better marksmen available, why choose Ray?
Ray was a small-time crook. How did he get the money to go to Europe?
Mr Posner, who has researched Ray's life more thoroughly than anyone, is convinced he received no money in advance but may have believed he would receive a large "bounty" afterwards. The author says Ray already had money from dealing in marijuana.
Ray would probably never have been traced were it not for one strange act. On leaving the boarding house, says the official version, he dropped the rifle and other objects traceable to him on the pavement wrapped in a bedspread. Why would an assassin choose to leave behind such evidence?
Mr Posner admits this act is hard to rationalise. He speculates that either Ray saw police cars and panicked or that an accomplice was meant to collect the gun and dispose of it but failed to do so.
Mr Pepper believes this is all part of what he calls "the set-up story".
If anyone other than Ray was involved in the murder - or if Ray was wholly innocent - those responsible are now either dead or reaching the ends of their lives.
Some maintain the truth lies locked in FBI files.
The 40th anniversary of the King murder - and the imminent arrival of a new US president - is prompting them to call for those files to be opened at last.