The IRA bombing at a Remembrance Day commemoration in the Co Fermanagh town of Enniskillen 20 years ago this week killed 11 people, injured 63 and repulsed the world.
Amateur video footage of the aftermath of the explosion on November 8 1987 was broadcast internationally, vividly portraying the suffering of innocent victims.
Half were Presbyterians who had inadvertently stood the closest to the hidden 40lb device so that they could be convenient to their place of worship.
There were three married couples – Wesley Armstrong (62) and wife Bertha (55), Billy Mullan (74) and wife Agnes (73), Kit Johnston (71) and wife Jessie (62).
The others who died were Sammy Gault (49), Ted Armstrong (52), Johnny Megaw (67), Alberta Quinton (72) and the youngest victim, Marie Wilson (20).
A 12th person, Ronnie Hill, who slipped into a coma days after the explosion, never woke up and died almost 14 years later.
For the first time in the Troubles, the IRA admitted it had made a mistake, planting the device in a building owned by the Catholic church to, they said, target security forces patrolling the parade.
The bombing is believed to be one of the watershed incidents of the Troubles largely because of the international outcry against the violence.
The then secretary of state, Tom King, called it "obscene and debased" while US President Ronald Reagan said all of America joined him in his "revulsion".
Cardinal Tomas O Fiaich said that anyone involved in the bombing was guilty of "murder most terrible".
U2's Bono paused during a rendition of his protest song about the Troubles, Sunday Bloody Sunday, to denounce the violence and the Irish-Americans who supported it.
"Where's the glory in bombing a remembrance day parade of old-age pensioners, their medals taken out and polished up for the day?" he asked.
"Where's the glory in that? To leave them dying, or crippled for life, or dead under the rubble of the revolution that the majority of the people in my country don't want."
In the aftermath of the bombing the Fermanagh brigade of the IRA was stood down and support for Sinn Féin diminished.
In the council elections of 1989 the number of seats held by the party halved from eight to four.
But despite all the condemnation, nobody has ever been charged for the Remembrance Day bombing.
One man, Charles Caulfield – originally from Scotstown in Co Monaghan but now living in America – was named in Parliament by the former Ulster Unionist MP Roy Beggs as the mastermind behind the bombing.
Republican sources, however, have dismissed his involvement.
On the 10th anniversary of the bombing Sinn Féin leader Gerry Adams publicly apologised for the atrocity.
This week a statement from the party said that the attack had been "a huge tragedy".
"There are still many people who feel the pain and loss of 20 years ago as if it was yesterday," it read.
"Today the political process has delivered real hope and the reality of a positive post-conflict arena.
"Sinn Féin are absolutely committed to seeing a process developed which can deliver closure for the families of all those killed during the conflict, including Enniskillen."
One of the most striking aspects of the aftermath of the bombing was the way many of the victims' families dealt with – and continue to deal with – the tragedy from a Christian point of view.
The most famous example of this was Gordon Wilson, who said he bore no ill will towards the bombers who killed his daughter Marie.
He went on to meet face to face with IRA leaders to appeal for them to stop their violent campaign and he later became a senator in the Republic.
The Rev David Cupples, minister of Enniskillen Presbyterian Church, believes the unprecedented media coverage of the bomb coupled with the Christian reaction from the families transformed it from a tragedy to a turning point in the Troubles.
"The people were trying to deal with it from a Christian point of view and that contrasted with the action of the bombers so the moral and spiritual aspect of these issues came to the fore in the Enniskillen bomb as it didn't in any other," he said.
Although the bombing is being reinvestigated by the PSNI's Historical Enquiries Team, Mr Cupples believes the issue of prosecution has "come and gone".
"As a matter of social justice, any crime should be fully investigated until there is no other line of inquiry," he said.
"But on the level of pragmatism the police are facing a wide range of challenges.
"New crimes are being committed all the time and the Enniskillen bomb is receding further and further into the past.
"Against that background one would understand why an event of 20 years is not top of the agenda."
A memorial service in the Presbyterian church, which many of the victims and injured belonged to, will be held this Thursday on the 20th anniversary.
"The clergy involved believe the actual service will help the injured and bereaved and the fact that they will all be together will be a source of comfort," Mr Cupples said.
"At some stage there has to be some sense of closure and I would be surprised if any further services take place.
"I doubt there will be anything on the 30th anniversary, possibly because many of the people connected to it will have died.
"I feel, and this is only a hunch, that the events of this 20th anniversary may be the last major public acknowledgement of the bomb."