In Belfast like everywhere else on the planet, it was the 9/11 moment of the Sixties – the flashback freeze-framed for ever in time and place in people's memories from 50 years ago today when the killing of one man in America sent a collective shockwave around the globe in a way that only the murders of thousands of innocents in the Twin Towers would ever equal in their sheer awesome and awful enormity.
Few people of a certain vintage who were alive on November 22, 1963, will ever forget where they were as they first heard the news or the fear that gripped them as they tried to fathom just what the assassination of President John Fitzgerald Kennedy would mean for the world as a whole or for their worlds in particular.
In the technological wilderness before satellites, Skype, and instant rolling 24-hour news, the questions about the assassination's perpetrators and motives were on everyone's lips but the answers came slowly as news organisations took time to beam the grainy pictures and equally blurred analysis of the shooting in Dallas into homes here which were lucky enough to have television. Even now the footage of Walter Cronkite removing his glasses just before he told TV audiences "From Dallas, Texas, the flash, apparently official, 'President Kennedy died at 1pm Central Standard Time'" still makes for emotional viewing.
The impact in Ireland was seismic. Kennedy wasn't only the great new hope for peace and progress but he was also one of ours. Well almost.
Nationalists adored him. Unionists weren't quite so sure. He was, after all, the first Roman Catholic to hold office in the White House and he was an Irish-American to boot.
On top of all that he'd also metaphorically wrapped the green flag around him during an emotional visit to his roots in the Republic five months earlier in June 1963.
No man before or since has received a céad míle fáilte quite like it on the island and it's said the pin-up President was planning a lower key return but his assassin
Lee Harvey Oswald put paid to that and to the life of the man who needed only his initials to identify him.
No matter about the unionist politicians' suspicions about JFK, thousands of 'ordinary' people in Northern Ireland were horrified by his murder and queued outside the old American consulate in Belfast's Queen Street to show their disgust by signing a book of condolence for the President.
The newspapers reflected the mood of anger and anxiety.
The Belfast Telegraph splashed the breaking story on the front page of its late final edition and in an editorial said: "The world is greatly the poorer of an outstanding leader who served America and the free peoples with courage and ability and who has been shot down senselessly because he was seeking to ease racial attitudes and tensions."
Such was the reliance on the written word for information about the assassination, that extra copies of the newspapers were printed to meet the demand.
Even the Russians showed their respect as a Soviet cargo ship the Repino flew its flags at half-mast in Belfast docks.
The speculation over who killed JFK and why was fevered as the pictures of the slain President slumping in his open-top Lincoln Continental convertible beside his blood-splattered wife Jacqueline were run and re-run on the news on the only two channels on televisions here.
But as millions sat spellbound in their living rooms, there was even more drama about to explode in front of the watching world's eyes and trigger thousands more conspiracy theories which are still the subject of heated debates half a century later.
Live television pictures showed Lee Harvey Oswald, a former Marine who had once defected to Russia, being led out of Dallas police headquarters and suddenly nightclub owner Jack Ruby stepped out of the crowd to shoot him at point blank range.
Ruby said he killed Oswald to save Jackie Kennedy the ordeal of having to go through a trial.
In Belfast, a number of sporting events were cancelled and promoters said people just weren't in the mood.
But the show did go on at Belfast theatres where comedian James Young was starring in a comedy called An Apple A Day at The Group and a new Sam Cree farce For Love Or Money was staged at The Arts.
Requiem Masses were celebrated for the President at a number of Catholic churches around Belfast, Newry and Londonderry, and 600 people attended a special service in St Anne's Cathedral.
Then four days after the assassination, Stormont paid homage to JFK too.
Prime Minister Captain Terence O'Neill, who had earlier sent a telegram of sympathy to JFK'S Attorney General brother Robert, led the tributes but he was one of the few unionists to speak. Nationalists like Eddie McAteer and Cahir Healy made impassioned speeches in the House about the influence of the President who they said had been fearless in his quest for peace.
The American Consul General Eric Hughes was in the House to hear the Stormont MPs praise the President.
And this week the wheel almost turned full circle but it was local politicians who listened at Stormont to the current American Consul General Gregory Burton as he lauded JFK. Mr Burton wasn't quite three-years-old at the time of the killing but he told me he has clear recollections of his grandmother urging him to be quiet so that his family could watch the funeral on television.
"That is my very first memory," he said. "It is still emblazoned on my mind."
Mr Burton said JFK broke the mould of presidents. "He was the first television President with a big presence who used the media well and became more accessible to most Americans. His popularity was unparalleled."
At Stormont the Great Hall was turned into a mini-cinema for the first time as Mr Burton introduced a special preview screening of a new Kennedy film Parkland about the chaotic events in the hospital of the same name after he was shot.
He also recalled that JFK's brother Edward had visited Stormont in 2007.
Assembly members joined several hundred members of the public to watch the drama. Speaker Willie Hay said he remembered the assassination having a huge impact not only in America but right across the world as an inspiring young leader was cut down before he could fulfil his potential.
Mr Hay, who visited the John F Kennedy Library and Museum in Boston two years ago, paid tribute to the role that successive US Governments had played in the peace process here. "We have had no greater friend than the American people and their administration." Among the audience was the Rev Mervyn Gibson, the Orange Order chaplain who is representing the DUP at the talks on parades, the past and flags hosted by another prominent American, Dr Richard Haass.
"I don't remember the assassination," says Mr Gibson, "but I do recall how Ireland was fascinated by Kennedy. No matter where you went in the Republic there were pictures of Kennedy and the Pope in every window.
"As I grew up I started to take an interest in what happened to Kennedy but the conspiracy theories bore me." But that wasn't the case with Belfast community development worker Michael Briggs.
"I was born in 1963 and my father was intrigued by him," he said. "I once went to a meeting in Toronto of conspiracy theorists but it was a real head-melter. I was more interested in finding out if the American Government were involved in his death."
Assemblyman Sammy Douglas was a 10-year-old boy in Sandy Row when JFK was shot. He recalls: "I was standing in Blythe Street when someone said that the American President was dead. I remember the shock of it all as if it were only yesterday.
"But his death didn't have much of an impact in Sandy Row."
Brian Small, a fundraiser for integrated education here, also says the memories of the assassination are as clear today as they were 50 years ago.
"I was a trainee store manager in Ayr and I'd just come back home when the news came on TV. It was a cathartic moment in my life."
Mr Small is a regular visitor to Dallas and has visited the Book Depository from where Oswald launched his attack. "Standing at the very window where he was and looking down on Dealey Plaza and the grassy knoll was very eerie."
Also in Dallas recently was MLA David McIlveen who was deeply moved as he stood at Kennedy's grave beside an eternal flame at Arlington National Cemetery.
He says: "It was a world-changing event in terms of the magnitude of what happened and at the cemetery you can still feel the emotion that comes from it."
Malcolm and Kay Telford from Carryduff say they have lost count of the TV programmes on the Kennedys they have watched. "I'm no closer to establishing the truth," says Malcolm, before Kay admitted that her interest on the Kennedys centred as much on the First Lady as on her husband.
She's not alone. And Belfast has its own bizarre memorial to her in the shape of an amusement arcade in the city centre called Onassis which is on the site of the former Harland and Wolff social club she visited with her second husband – shipping magnate Aristotle Onassis – in 1970.
'Our home was plunged into sombre silence'
Ivan Little was just 11, but he'll never forget the moment
I can remember the exact step on the stairs where I was standing when I heard my mother shouting out that Jack Kennedy had died after a shooting.
In my youthful naivete – I was 11 – I initially thought mum was talking about a neighbour of ours in the Stormont area.
Our Jack Kennedy whose real name was also John played in goals for Distillery and later Glasgow Celtic.
But the penny soon dropped and the mood in our house swiftly changed.
The plan had been to celebrate my mother's birthday on Friday, November 22 but instead the house was plunged into a sombre silence.
We watched what news there was on the television and in the coming days saw the funeral but I can't be sure if my recollections of live pictures of Jack Ruby gunning down Lee Harvey Oswald were just tricks of the mind.
In St Augustine in Florida in 1995 I visited the oddly named Museum of American Tragedy which boasted that two of its cars were used by the President and his killer on that fateful day in Dallas in 1963.
Also on show was an ambulance which was said to have been the very one in which Oswald died.
But like so much of the Kennedy story, I've no idea if the claims were fact or fiction, fantasy or fib.