Image caption The IRA considered the lab a key target because of its role in analysing evidence in terrorist cases

It was one of the biggest bombs the IRA ever detonated, comprising an estimated 3,000lbs (1,360 kg) of home-made explosives.

Twenty-five years ago, Northern Ireland's forensic science labs at Belvoir Park in south Belfast was targeted.

The IRA considered the lab a key target because of its role in analysing evidence in terrorist cases.

The group's aim was to deal a devastating blow to the criminal justice system by destroying forensic evidence set to be used in future court cases.

Media playback is unsupported on your device Media caption Damage caused by the IRA bomb at the NI science lab in Belvoir Park. Archive footage.

But the bomb had a massive blast zone, damaging more than 700 homes and other buildings within a mile-and-a-half radius.

'Completely gutted'

Jim Armstrong, a recently retired principal scientific officer who worked at the labs at the time, was initially convinced the IRA had achieved what it set out to do.

"I can remember that later on that night, a senior member of staff from the laboratory contacted me and said there had been an explosion and would I still come in the next day to help get things up and running again," he recalls.

"I remember turning up and thinking that what I would see would be a little hole in the ground and a couple of broken windows.

"What I actually saw was this devastation, the place was completely gutted.

Image caption 'I thought this is this laboratory finished, we are finished here' recalls Jim Armstrong, a scientific officer who worked at the labs in 1992

"I remember this wise guy standing beside me saying: 'Forget about being a forensic scientist for the next months, we're now in the construction industry.'

"I just thought the lab had been completely destroyed. I thought this is this laboratory finished, we are finished here."

A large crater on the road at the front of the building marked the spot where the huge van bomb exploded.

The front of the building was almost destroyed.

Image caption A large crater on the road at the front of the building marked the spot where the huge van bomb exploded

The damage was so severe that media commentators, security experts and lawyers assumed that the forensic evidence it contained had been destroyed.

Belfast solicitor Joe Rice was one of those who expressed concern about the possible impact.

Speaking to the BBC shortly after the explosion on 19 September 1992, he said: "Where forensic evidence has been damaged or lost, there will be an onus upon the police and, ultimately, the director of public prosecutions to re-examine the overall evidence in the case.

Image caption Internal damage to Northern Ireland's forensic science labs at Belvoir Park in south Belfast

"So it may well be that cases may be withdrawn, cases may be dropped.

"It depends of course how fundamental the forensic evidence is in respect of each individual case."

The government and criminal justice agencies remained tight-lipped about the extent of the damage to forensic evidence and exhibits.

That fuelled the speculation that the IRA had achieved its aim.

'We got lucky'

Image caption The main part of the lab was severely damaged

But now, a quarter of a century later, Jim Armstrong says the IRA failed because it targeted the wrong part of the building.

"It was chance," he said. "They put the bomb in the wrong area."

"If they'd moved the bomb to the back of the building then, yes, that would have been the area where the exhibits and the case files were stored.

"We just got lucky."

An aerial photograph taken shortly after the explosion supports his claim.

Image caption An aerial photograph supports Jim Armstrong's claim that the IRA failed because it targeted the wrong part of the building

It shows that while the main part of the lab was severely damaged, a rectangular building at the south-east perimeter of the site was largely untouched.

This was where the forensic exhibits and reports were stored.

"The main impact was that you weren't actually doing the science anymore," said Jim Armstrong.

"What you were actually doing was digging and digging and lifting and recovering exhibits and moving them off site to a different storage area."

"It took us out of action for about six weeks. Within a few months we were pretty much back to normal.

"It actually had very little impact on the science and the judicial system."

Image copyright Joe Rice Image caption Solicitor Joe Rice said there was 'unfounded' speculation the bomb would significantly hinder the prosecution of cases

Solicitor Joe Rice said the fears that he and others had about the impact on the court system were not realised.

"There was a lot of speculation at the time that this would have quite a significant effect on the prosecution of cases," he told the BBC this week.

"It's now fair to say that those fears were unfounded.

"There may have been some delays, I imagine, in the processing of cases, and the gathering together of evidence and forensic reports flowing from the evidence, but in real court terms there was no real delay."

In the weeks after the explosion, Jim Armstrong and his colleagues moved their forensic exhibits and equipment to what was supposed to be a temporary new home at Seapark near Carrickfergus.

They are still there, in a new £11.5m purpose-built forensic science lab.

The number of scientists working in the labs has more than doubled from 80 to 180, and forensic science has also moved on in ways that could not been have been imagined when the Belvoir site was attacked.

"We now have a very modern purpose-built laboratory that probably puts us as one of the best providers of forensic science services in the world, I think," said Jim Armstrong.