It resulted in the deaths of 29 innocent people from many different backgrounds, including a woman who was pregnant with twins, and left hundreds more seriously injured.
Responsibility for the carnage lies squarely with those who planted the device, but there have been increasingly firm indications that the security authorities had at least some advance knowledge of what was planned and might even have prevented it from happening.
While this has all been an appalling vista for the relatives of the victims, they have conducted themselves with enormous dignity as the years have gone by and a range of serious developments have emerged.
The memorial ceremony which took place in Omagh's memorial garden on Sunday was intensely moving and demonstrated the courage and resilience of all those who lost loved ones in the carnage on the town's Market Street.
Flowers were laid at a stone bearing the names of all the victims and there were readings in three languages, English, Irish and Spanish, in respect of the nationalities of those killed
Michael Gallagher, who lost his son Aidan at the age of 21, was entitled to say that the service, organised by the Omagh Churches Forum, showed people were unified.
He said the attendance was a "powerful testimony to community spirit and cohesion 25 years after our small town was ripped apart".
What has been hugely disturbing for all concerned is that, despite all the assurances offered from the day and hour of the catastrophe by those in positions of great influence, no one has ever been criminally convicted of involvement in it.
Four men were named and found liable for the attack in a landmark 2009 civil case brought at the High Court in Belfast by some of the grieving families, but that could never have been the end of the matter.
In February last, in response to a long-running campaign by the relatives, secretary of state Chris Heaton-Harris finally announced the staging of an independent statutory inquiry which may open either later this year or in early 2024.
It can only be fervently hoped that all the key issues will be examined in comprehensive detail, providing the people of Omagh with the answers they have deserved since the horrendous events of August 15, 1998.