'They've killed my husband. I have his brains in my hand.'

Nick Morrison looks at how the assassination of JFK changed the world.

THE first one was mistaken for a misfiring motorcycle; when the second one followed almost instantly, all doubt was gone. Six seconds later there was a third, and this one killed President Jack Kennedy. Just as the ripples in a pond spread out long after the stone hits the bottom, so the effects of those three shots are still being felt today.

As the youngest man to win the US Presidency, Kennedy embodied the hopes of a new generation, sweeping away the stilted formality of his predecessor, Dwight D Eisenhower, and ushering in a bright new era. He replaced torpor with vigour, surrounded himself with lean academics instead of well-fed businessmen and exchanged military bearing for confident style. He was good-looking, charismatic and glamorous; not for nothing was the Kennedy White House christened Camelot, a court attracting a new breed of high achievers to pay homage.

His death brought that new age to a shuddering halt. Despair followed disbelief followed shock as the enormity of the effects of those shots in Dealey Plaza began to sink in. Most Americans knew their president had been shot before they heard the confirmation of his death, as the news was broadcast to an incredulous world. The average American was reckoned to have watched 32 hours of television that weekend.

Forty years on, the power of the assassination to shock, and the Kennedy myths which sprang up subsequently, fuelled by conspiracy theories, have scarcely diminished. "Where were you when you heard Kennedy had been shot?" is still a question that resonates with anyone over 50. Kennedy may have died that day in Dallas, but a legend was born. The British Library lists 314 books with John F Kennedy in the title; countless more are devoted to his presidency, and more pertinently, his death.

It was 11.40am on Friday, November 22, 1963, when Kennedy arrived at Love Field in Dallas, the departure point for the motorcade which would attempt to improve the President's ratings in a key state. Kennedy had narrowly won Texas in the 1960 election, when his majority over Richard Nixon was the smallest in presidential history, but his controversial civil rights bill had cost him support among Southern Democrats.

At 11.50am, the motorcade started, with Kennedy and wife Jackie sitting in the back of a 1961 Lincoln Continental limousine, Texas Governor John Connally and his wife Nellie in the jump seats behind the driver, with both women sitting on the driver's side.

At 12.30pm, the President's limousine turned into Elm Street and started down the hill at 11mph, heading to a railway overpass in Dealey Plaza. Mrs Connally turned around and said: "Mr President, you certainly can't say that Dallas doesn't love you."

Almost immediately, there were three shots. The first is thought to have missed and ricocheted harmlessly away, but the second passed through JFK's neck and into Governor Connally's chest. The third, six seconds later, hit the President in the head.

The entry wound was high up on the back of the skull: the assassin had come within centimetres of missing the President. Instead, pieces of Kennedy's skull exploded into the limousine and onto the road, and blood covered the roses the two women had been given when they arrived in Dallas, yellow for Mrs Connally, red for Jackie Kennedy. Nellie Connally, the only passenger in the Lincoln still alive today, heard Jackie Kennedy cry out: "They have killed my husband. I have his brains in my hand."

In the Zapruder film, the 26 seconds of grainy footage which captured the final moments of JFK's life, Mrs Kennedy is seen scrambling onto the boot of the limousine, trying, she said, to collect pieces of her husband's skull, as a Secret Service agent tries to get in the car and shield the President.

The Lincoln sped towards Parkland Hospital, arriving at 12.36pm. JFK and Governor Connally were taken into separate rooms. Connally was wounded in his back, chest, wrist and thigh but survived. Kennedy had a wound in his neck and his head. A priest performed the last rites and he was pronounced dead at 1pm. He was the fourth American President to die from an assassin's bullet.

Three minutes after the shooting, Lee Harvey Oswald left the Texas School Book Depository, overlooking Dealey Plaza. Less than 45 minutes later he murdered a police office trying to arrest him, before he was seized after a scuffle in a theatre at 1.50pm.

At 2.15pm, the President's casket was loaded onto Air Force One at Love Field, the starting point for the motorcade. As the plane headed towards Washington, District Judge Sarah T Hughes swore in Lyndon Johnson as the 36th President of the United States.

The following day, Oswald was charged with murdering the President. A rifle had been found on the sixth floor of the book depository, with three shell casings nearby and Oswald's prints on the barrel. But on November 24, two days after the assassination, Oswald was being transferred to the county jail when he was shot and killed by Jack Ruby, a night-club operator.

A week after the killing, President Johnson established the Warren Commission to investigate, but its conclusion, submitted the following September, was not enough to quell the already burgeoning band of conspiracy theorists, encouraged by the many inconsistencies and suspicious circumstances.

Some eye-witnesses reported hearing shots coming from a grassy knoll on Dealey Plaza; some saw a puff of smoke; others reported seeing two men behaving suspiciously in the same area. The second bullet, which hit both the President and Governor Connally, was mysteriously intact for one which had caused such damage. Doubts were cast on Oswald's ability to get from the sixth floor to the second floor in the time between the shooting and being seen by a policeman. In the three years following the assassination, 18 witnesses died in mysterious circumstances.

And the list of conspirators has run from the Mafia, fearful that Kennedy and his Attorney General brother Bobby would crackdown on organised crime, to the CIA, hostile towards a liberal President. But no other gunmen have been found, and no one has been convincingly blamed. As with Marilyn Monroe and Princess Diana, there is a reluctance to accept that the death of a hero can have a simple explanation, in JFK's case that of a lone gunman, with his own twisted motivation.

And what of the other passengers? Jackie Kennedy continued to nurture her husband's memory, until marrying shipping magnate Aristotle Onassis. She died in 1994, a year after Governor Connally, who recovered from his injuries but later suffered from a lung disease, thought to have been brought on by scarring from the bullet wound. Nellie Connally is 84 and this year brought out a book about her memories of that day. As for Jack Ruby, he was convicted of the murder of Oswald but appealed and died still waiting for a second trial.

John Fitzgerald Kennedy would have been 83 if he had lived. But had he lived, he may have been seen quite differently. His civil rights legislation had made him unpopular in the South, traditional Democrat stronghold, and he seemed to be heading for defeat in the 1964 election. And while he may have faced off Kruschev in the Cuban Missile Crisis, he was also responsible for escalating military involvement in Vietnam, heralding an experience which was to scar an entire nation. The signs were there that he would be a one-term President, leaving his followers disappointed and his opponents derisive.

Instead, he is the President who was cut down in his prime; a President whose great promise was unfulfilled but whose star has never dimmed.

Those three bullets may have ended his Presidency, but they have given him an immortality he could otherwise have never hoped to achieve.