IN death, Seamus McKenna is an unlikely hero, a man who, according to the dissident Republican Network for Unity, had nobly spent his life "confronting partition and British rule in Ireland" and a man worthy of a paramilitary funeral last week.

In reality, his life was, by McKenna's own admission, "a largely unhappy existence". Not only was he very strongly suspected of driving the car bomb into Omagh that lead to the deaths of 29 people and two unborn children in 1998, he was also a chronic alcoholic and a lonely, isolated man incapable of holding down work for more than a few weeks at a time.

I got to know him very well over the last two years. As an attorney in New York, I had discussed with some wealthy Irish-Americans the possibility of McKenna giving evidence against one of the accused in the Omagh case – the last-gasp attempt to finally win some convictions in the worst atrocity of the Irish Troubles.

I first tracked him down to Simon Community-supported housing in Dundalk, where he had been living after splitting with his wife Catherine. I left a note under his door and he called me several hours later. In the window, I could see a pair of pants and a crinkled shirt drying in the living room and an empty can of beans and an unwashed plate on the table. Several of the men in nearby accommodation were long-term alcoholics who, like McKenna, would be homeless without subsidised housing.

I met him the next day, New Year's Day 2011, at a Chinese restaurant in Dundalk.

He was wearing the khaki pants and chequered shirt that had been hanging in his living room and was wearing a smart pair of glasses. He looked nothing like his post-Omagh mugshot, when he was dragged into a police station still in a building site woolly jumper and unkempt, hopelessly outdated Seventies-style sideburns.

Over a meal, McKenna asked me why I had come all the way from America to see him. I said that I and many other people would be willing to help him out if he was willing to give evidence.

"About what?" "About events 13 years ago," I said. "Events 13 years ago" needed no further explanation. "Ah . . . no, I don't think I could do that," he said, but added that he was willing to listen.

He was so nervous about any mention of the word "Omagh" that his hand would jitter and he would stumble to take a swig of his drink, so we used alternative phrases like "the thing that happened" or, as he preferred, "the civil action". (He was the only one not found liable in a civil action taken by victims' families against five of the bombers – the others included McKenna's building company boss Colm Murphy and his workmate Seamus Daly.)

He told me that, as a result of the bombing, he had been barred, at least temporarily, from many of the pubs in Dundalk. "But not this one," he said with pride, referring to the pub to which we had walked after our meal, as he ordered yet another pint of the Dutch lager he loved because, so he claimed, it gave a less severe hangover than Harp. When he drank, he would open his mouth fully to meet the pint glass and take in a giant mouthful between his lips. If too much went in, he would blow some back into the glass before wiping his mouth and look at me through bleary, worn eyes.

He said that he could not give evidence on Omagh because it had taken him so long to rebuild a relationship with his family. I asked if his concern was security for his family or loss of esteem in their eyes.

"Loss of esteem," he said bluntly. "I would give everything I have to bring my father back to life, I don't want to lose my son."

Although largely isolated, he found company in animals. His neighbour said McKenna left out bread for the wild birds in the winter and took great satisfaction in watching them eat it. "Sure who else would feed them?" McKenna said to me once.

Just when I was starting to enjoy his conversation, the depravity of Omagh would come back to mind. He had a habit of sitting sideways as he drank, and as he lifted his pint, it occurred to me that the hand in front of me is the one that allegedly changed the gears in a stolen Vauxhall that exploded in Omagh, killing the son of my friend Michael Gallagher, destroying three generations of the Grimes family, leaving Liz Gibson without a sister and permanently blinding Claire Gallagher, a talented young pianist.

"What do you think of the Omagh bombing?" I once asked in a pub in Dundalk in May 2011.

"Do you think, like Padraig Pearse, that the blood of the people has to flow or do you think it was an atrocity?"

"I think it was a terrible thing," he said. "But having said that, I would like to see British soldiers shot dead and I'd like to be the one pulling the trigger."

"To what end?" I asked. "What better society can be created by killing more soldiers?" "I don't know," he said, "but like I say, I'd like to be the one pulling the trigger."

So much of his limited self-esteem was caught up in the republican cause that it was impossible for him to let go, and after a split in the Continuity IRA, he sided with the more militant Oglaigh na hEireann. He wasn't a boaster or a hard man like some IRA members, but he enjoyed a certain menace. "If you had approached me like this 10 years ago, you'd have been shot," he told me over and over until I told him to shut up and deal with the present reality of his life.

When he was drinking, he made clumsy, pathetic moves on women. At closing time one night, the barmaid opened the door to let us out. "Ah, pet you're great," said McKenna, giving her a huge hug and refusing to let go, while pushing his body as close as possible to hers. She looked over her shoulder and grimaced at me. I told him we had to go. "Good girl," said McKenna. "Good girl," repeating it until I gripped his arm. "Jesus, great knockers," he said to me as explanation for this excruciating scene.

The next morning, instead of joining my girlfriend and me at a local cafe for breakfast, he was already in the pub.

"Ye carry on, come over to the pub after," he said. When we got there at 11am, he was already drunk, and leering all over my girlfriend, breaking off conversation with me to stare at her buttocks when she went up to the bar. He then asked her to come to his house to see "my wee dog. You'd like him. Come to my house any time," he said, while wiping lager from his lips.

Despite the international outrage over Omagh, he soon got over his six-month-long self-pitying bender and was back building car bombs. In 2003, he was caught red-handed with some of the other suspects building a 1,000-pound car bomb – twice the size of the Omagh bomb.

He found himself in Portlaoise jail with his old boss, Colm Murphy, who was in on unrelated charges and whom he found "quiet and very withdrawn, a bit odd really".

Although he liked Murphy, he had nothing but disdain for Liam Campbell, the officer commanding of the Real IRA and the man who allegedly made the last of the vague warning calls on the day of the Omagh bombing. Campbell blamed McKenna for giving unclear details of the car's locations to the rest of the bomb team. I asked McKenna directly why he didn't like Campbell. "Why do you think?" he said bluntly.

Most upsetting for McKenna, and the other disaffected foot soldiers of the dissident terror groups, was the Criminal Assets Bureau investigation into Campbell, which revealed that he had more than €800,000 in the bank, a network of other payments to close associates, and at least five properties. (Not to mention 96 magnums of champagne found in his cow shed).

"And we had nothing," said McKenna. He said that he and now deceased Omagh suspect, Kevin 'Kiddo' Murray, and even Real IRA leader, Michael McKevitt, realised too late that Campbell was using the Provisional IRA, and then the Real IRA, to disrupt security services along the border while he creamed off vast profits from smuggling. Their phoney war, which lead to the deaths of so many innocent people, had been a giant scam.

McKenna admitted it one night, when he was preparing to walk to his sad little apartment. He could not afford a taxi and could only stagger home. "Campbell did us all in," he said though sad eyes. "And we have nothing left. Nothing at all."

Sunday Independent