Suite 850 at the Texas Hotel in Fort Worth. It is the morning of November 22 1963 and John Fitzgerald Kennedy, 35th president of the US, is preparing for his short flight to Dallas.
Kennedy needs to woo Texas if he is to beat off Barry Goldwater, the Republican senator likely to be his opponent in the presidential race of 1964.
But Dallas is a hotbed of extreme conservatism, the only major city in the US to have voted for Richard Nixon instead of Kennedy in 1960 and, now, here the president stands, with a copy of today's Dallas Morning News. It carries a black-edged advertisement "welcoming" the president. The ad consists of a list of accusatory questions:
Why is the Kennedy administration approved of by the US Communist Party?
Why is the CIA being asked to arrange coups against Washington's anti-Communist allies? And so on.
Jack Kennedy turns to his wife, Jackie: "We're heading into nut country today," he says. Then, pacing the room, he thinks aloud: "It would not be a very difficult job to shoot the President of the United States. All you'd have to do is get up in a high building with a high-powered rifle with a telescopic sight, and there's nothing anybody could do."
Just over two hours later Kennedy is killed in the way he prophesied.
This Friday in Dallas, the 50th anniversary of the assassination will be marked with the tolling of church bells, a ceremonial fly past and readings of Kennedy speeches.
"This is the moment when the Kennedy assassination tumbles over that dusty border dividing current affairs from history," said Anthony Summers at his riverside home in rural county Waterford, in Ireland. He is squeezed between shelves crammed with files marked "JFK", the product of research that began in the 1970s and continued until this year.
The Kennedy assassination was one of the first literary peaks he set out to scale. His efforts resulted in the 1980 book Conspiracy, which has been reworked and republished with the title Not in Your Lifetime, a reference to Earl Warren, chief justice of the US, who headed the original inquiry into the JFK assassination.
In 1964, when asked if all the information uncovered by his investigation would one day be made public, he replied: "Yes, there will come a time - but it might not be in your lifetime."
Why not, if, as the Warren Commission concluded, the chief executive of the US was murdered by an alienated misfit called Lee Harvey Oswald acting alone?
Sanders now has a name, of a man who fits the bill as Kennedy's killer and is said to have confessed his involvement in the assassination before being killed in a commando-style raid on Cuba.
"Evidence that Oswald fired is pretty strong but also full of weaknesses. Why, if it was Oswald alone, do 1171 CIA documents on the subject remain classified in 2013?
"There is no doubt that something is still being concealed."
The US House Committee on Assassinations in 1979 concluded that Kennedy had "probably" been the victim of a plot, a second gunman being involved.
Who is Summers' candidate for "second trigger"?
In 2007 Summers and Robert Blakey, formerly chief counsel to the House Committee on Assassinations, interviewed 81-year-old Reinaldo Martinez Gomez, a Cuban exile living in Miami.
Martinez told them of a friend from student days called Herminio Diaz Garcia. A crack shot, he had been head of security at a casino in Havana run by the Mafia boss Santo Trafficante. He was also a political assassin, responsible for as many as 20 deaths. At the time of Kennedy's killing he was in the US.
Martinez said that, while detained in one of Castro's prisons, he had met Tony Cuesta, leader of an anti-Castro raid on Cuba in 1966 that had ended in Diaz's death.
Cuesta, who was badly wounded, told him about the night of the abortive raid and the words uttered by Diaz that he would never forget.
Said Martinez: "Herminio confessed to Tony Cuesta that he had taken part in the death of the US president."
Years later, in Florida, Martinez heard the same from another source, an old friend and fellow Cuban exile, Remigio Arce.
"The one who killed the president was our little friend." said Arce.
"Diaz ticks the boxes," said Summers. "He was a known political assassin and marksman, and had worked for Santo Trafficante, one of the two prime suspects in the assassination, along with fellow Mafia boss Carlos Marcello, who was named by the House Assassinations Committee.
"The Mafia had every motive to do away with President Kennedy. They were being pursued as never before. And a large part of the anti-Castro movement felt betrayed by Kennedy."
So where does Oswald fit in? "There is subterfuge by the CIA in regard to Oswald's visit to Mexico City a month before the assassination."
Surveillance tapes that record Oswald's visit seem to have been wilfully destroyed.
"I am absolutely not one of those who believes the CIA killed Kennedy. But I am sure they've hidden something."
The case refuses to go away, even after half a century. Summers, though, has had enough.
"After November 22 I don't want to hear about the JFK case again. It is a nightmare to work on, not only a labyrinth but a labyrinth with lots of turnings off the labyrinth. We don't know the answer and probably never will."
