The brother and widow of 37-year-old Dermot Hackett, who was shot dead by the UFF near Omagh, Co Tyrone in 1987, met Stone to find out the truth behind allegations in his autobiography that he did not murder the father-of-two.

Sylvia and Roddy Hackett shocked the convicted mass murderer by offering a gesture of Christianity after he said that he did not kill their late husband and brother.

However, Stone did admit that he arranged Hackett's murder and said he would have "pulled the trigger" if he had been present.

The extraordinary encounter secretly took place at Ballywalter in the Ards Peninsula for a forthcoming BBC Two series called Facing The Truth which brings victims and perpetrators of violence in the Troubles together for the first time.

For nearly 20 years, the Hackett family has been tormented by the senseless and brutal way in which Dermot died. They wanted to meet Stone for two reasons; to find out why he believed Dermot had to die; and to prove that their loved one was an innocent victim.

Roddy Hackett said the meeting has helped "give the family closure" and even expressed sympathy for Stone.

"I was expecting him to come to the meeting acting 'the big man' but he looked pitiful when he hobbled in with his walking stick and I found myself feeling sorry for him, " he said.

Hackett added: "Dermot was an innocent victim and we wanted to know why he was killed, and if it was Stone who shot him. He [Stone] appeared genuinely remorseful and I believed him when he said he didn't kill Dermot."

The Omagh man also described how Stone was stunned when the Hacketts offered to shake his hand. It was a moment that even moved one of the most notorious terrorists in the history of the Troubles.

"My sister-in-law Sylvia got up and shook his hand first and it really took the wind out of his sails. Stone said I was a better man than he was because if the roles had been reversed he wouldn't have shaken my hand, " said Hackett.

The tense and emotional meeting was overseen by Archbishop Desmond Tutu, who headed South Africa's post-Apartheid Truth and Reconciliation Commission.

During the encounter between Stone and the Hacketts, the archbishop declared:

"It is God who is present in this moment."

Stone, a UFF member who became infamous for the 1988 gun and grenade attack which killed three men at Milltown Cemetery in Belfast, was convicted of Dermot Hackett's murder, as well as five others.

Roddy Hackett believes meeting Michael Stone has helped the family come to terms with Dermot's death.

"I don't think Stone would have said 'I didn't shoot him' and then added, 'but I would have shot him if I had been there' if he wasn't telling the truth, " said Roddy.

"In other words, Stone admitted he was involved in Dermot's murder by association but that he didn't actually pull the trigger."