A High Court judge in the UK has ruled Donegal man John Downey was an 'active participant' in the 1982 Hyde Park bombing.
It's after a civil action brought by relatives of four British soldiers killed in the attack in London.
The 67-year-old suspect - a convicted IRA member - was charged with the murders, but his prosecution at the Old Bailey collapsed five years ago.
Mr Downey had been given a letter by the British government which he was able to produce during his criminal trial, guaranteeing he wouldn't be prosecuted.
Announcing her decision in the civil case today, Mrs Justice Yip said: "This was a deliberate, carefully planned attack on members of the military.
"I have found that the defendant was an active participant in the concerted plan to detonate the bomb, with the intent to kill or at least to cause serious harm to members of the Household Cavalry."
A second stage in the case will now take place to determine the amount of damages to be awarded.
Solicitor Matt Jury said families of the victims didn't think they'd win - suggesting "justice has prevailed".
John Downey, from County Donegal, did not play any part in the trial.
However, he had filed a written defence in which he denied any involvement in the attack.
The Hyde Park bombing happened in July 1982.
Four British soldiers - Squadron Quartermaster Corporal Roy Bright (36,) Lieutenant Dennis Daly (23), Trooper Simon Tipper (19), and Lance Corporal Jeffrey Young (19) - were killed by a car bomb as they rode through the park in central London.
