Thomas McMahon, former volunteer in the South Armagh Brigade of the Provisional Irish Republican Army (IRA) and one of the IRA’s most experienced bomb-makers, is sentenced to life in prison on November 23, 1979 for the assassination of Louis Mountbatten, 1st Earl Mountbatten of Burma, and three others (two children and an elderly lady) at Mullaghmore, County Sligo.

McMahon plants a bomb in Shadow V, a 27-foot fishing boat belonging to Mountbatten at Mullaghmore, near Donegal Bay. Lord Mountbatten and the others are killed on August 27, 1979 when the bomb detonates. The other victims are Doreen Knatchbull, Baroness Brabourne, Mountbatten’s elder daughter’s mother-in-law, his grandson Nicholas Knatchbull and 15-year-old crewmember Paul Maxwell.

McMahon is arrested by the Garda, the Republic of Ireland‘s police force, two hours before the bomb detonates at a Garda checkpoint between Longford and Granard on suspicion of driving a stolen vehicle.

The IRA claims responsibility for the act in a statement released immediately afterwards. In the statement from the organisation they say, “This operation is one of the discriminate ways we can bring to the attention of the English people the continuing occupation of our country.”

McMahon is tried for the assassinations in the Republic of Ireland, and convicted by forensic evidence supplied by Dr. James O’Donovan that shows flecks of paint from the boat and traces of nitroglycerine on his clothes. He is sentenced to life imprisonment for murder on November 23, 1979, but is released in 1998 under the terms of the Good Friday Agreement.

Following his release, Toby Harnden in Bandit Country: The IRA & South Armagh (1999) reports that McMahon is holding a tricolour in the first rank of the IRA colour party at a 1998 IRA meeting in Cullyhanna. However, according to a BBC report, McMahon says that he left the IRA in 1990.

McMahon twice refuses to meet John Maxwell, the father of Paul Maxwell, who seeks him out to explain the reasons for his son’s death. In a May 2011 interview for The Telegraph, Maxwell states that he had “made two approaches to McMahon, the first through a priest, who warned me in advance that he thought there wouldn’t be any positive response. And there wasn’t. I have some reservations about meeting him, obviously – it might work out in such a way that I would regret having made the contact. On the other hand, if we met and I could even begin to understand his motivation. If we could meet on some kind of a human level, a man to man level, it could help me come to terms with it. But that might be very optimistic. McMahon knows the door is open at this end.”

McMahon likewise refuses requests from Nicholas Knatchbull’s twin brother, who lost an eye in the same explosion. The latter, however, has forgiven McMahon and other members of the IRA who committed the act.

McMahon’s wife has stated, “Tommy never talks about Mountbatten, only the boys who died. He does have genuine remorse. Oh God yes.”

McMahon lives with his wife Rose in Lisanisk, Carrickmacross, County Monaghan. He has two grown sons. He helps with Martin McGuinness‘s presidential campaign in 2011, erecting posters for McGuinness around Carrickmacross.