Twenty-nine people lost their lives, including a woman pregnant with twins
Omagh is marking the 20th anniversary of Northern Ireland's worst single atrocity.
Relatives of the 29 people killed when a car bomb exploded in the Co Tyrone town will attend a memorial service.
Stanley McComb, who lost his wife Ann, says the passage of time has not eased his pain or changed his opinion of the bombers.
"When you waken in the morning, the first thing is your wife should be with you. Your life's completely turned upside down.
"Put it this way. It makes you hate people, which I never did. They say it's a sin to hate but I do hate these people. I hate them," he admitted.
Dissident republicans, opposed to the Northern Ireland peace process, had planted the 500lb bomb.
The dead included a woman pregnant with twins, her 18-month-old daughter and her mother.
Three children from Co Donegal and two Spanish tourists were also killed.
Nearly 300 others were injured. Cars, lorries and a bus were commandeered to transport them to nearby hospitals.
Ethel McClintock, a paramedic with the Northern Ireland Ambulance Service, describes it as "the worst day" of her professional life.
"There was no sign of life with the first victim that we went to and then we were taken from that gentleman to a number of other people who were lying on the street.
"As we went from one to the next one, there were no signs of life for any of these people.
"The size of that atrocity, the number of lives that were lost and the number of people who came away with life-changing injuries, it was definitely the worst scene that I'd ever seen."
The fact that the bombing had occurred just four months after the Good Friday Agreement only added to the sense of shock.
With no one convicted by a criminal court, the bereaved and injured have been campaigning for justice for two decades.