The construction worker, a married man and father of two young children, had made a home for himself and his family on Woodbrook Lawn, Bray, Co Wicklow, for around three years.
But he’d made little effort to establish himself in the neighbourhood, lined with neatly trimmed bushes and mowed lawns.
“He was known as a weirdo,” one neighbour said. “You’d say hello to him and he’d ignore you, he wouldn’t answer you back or even look in your direction.”
“He used to go into local bookies a lot,” said one local man in Bray. “But he didn’t socialise round here. If he was a construction worker, he didn’t bother with others in his industry round here.
“He was an evil man who didn’t let anyone know who he was.”
A surprised resident described Mark as “very, very quiet” and as “a terrible nice man”.
She said: “He is only in the area a couple years. He had two little girls. I am on my own and he was the only one who came in to check on me when the real bad snow hit.
“He knocked in several times and asked if I was OK and if I needed anything from the shop.
“He was a really nice neighbour. When he moved in, he couldn’t have been nicer. He asked me would I hold his key for him in case anything happened, if the alarm went off or anything like that. His wife was always around, out walking. She is a really nice girl. He was very, very quiet. A terrible nice man.”
Asked if she could ever have imagined her neighbour would be caught up in such events, she replied: “No, I couldn’t believe it when I heard it.”
Another Woodbrook Lawn resident never had any concerns about Hennessy either.
She said: “I didn’t really know him. He kept to himself mostly. When I heard the name I didn’t even realise he lived just a few doors away. He was very polite, kept to himself, and there was never any indication of any trouble or anything like that.”
Last Night: In Rathmichael