The first of the three linked attempts to kill the president that fall was uncovered in late October, when an informant tipped the Secret Service about a plot to shoot him in Chicago.

It would be carried out by what the source described as 'Right-wing paramilitary fanatics'.

Kennedy had been scheduled to arrive at Chicago's O'Hare Airport on Saturday November 2 to attend the annual Army–Air Force football game at Soldier Field.

According to the informant, four sharpshooters would be hidden along the route of the motorcade as it made its way to the stadium.

But the Chicago branch of the Secret Service foiled the plot, found four rifles with telescopic sights inside a rented apartment and took two of four suspects into custody. Kennedy's trip was cancelled in response.

The two suspects were then released – but we have never been told why.

What we do know is someone else was slated in to take the fall – not the four snipers.

The echoes of Lee Harvey Oswald – who was charged with Kennedy's assassination in Dallas but claimed he was a 'patsy' – seem clear.

The name of the man in the Chicago plot was Thomas Arthur Vallee, a Korean War veteran.

Two months earlier, as Oswald was about to move from New Orleans to Dallas – where he got a job in a building overlooking the route of the presidential motorcade – Vallee landed a job as a printer in another tall building that overlooked Kenndy's planned route to Soldier Field.

Like Oswald, Vallee had connections with the secret services and with Cuban exiles. And, from his window at work, he would have had a view of the presidential limousine that was three levels lower and ten times better than Oswald's view from the Dallas School Book Depository.

There is another strange parallel: the motorcade in Chicago was scheduled to make a sharp turn right in front of Vallee's building, thereby slowing Kennedy's car to a crawl – a quirk of planning repeated in Dallas with fatal consequences.

The second attempt on Kennedy's life, in Tampa, was planned for later in the month.

It might seem curious that the three assassination attempts planned for Kennedy in November 1963 were in Chicago, Tampa and Dallas. But of course, these were cities under the control of Giancana, Trafficante and Marcello, three of Kennedy's most implacable Mafia opponents.

So, with Chicago and Tampa off the table, it had to be Dallas which, filled with his slot machines and duke boxes, happened to be the most important city in Mafia don Carlos Marcello's invisible empire.

What's certain, is this: from November 9 onwards, the FBI and the Secret Service not only knew of a serious plot to assassinate Kennedy, but exactly how it would be carried out. Yet still the trip to Dallas went ahead.