I did watch it and found it chilling in the extreme. I also felt sorry for the children of the two murderers, having to see their parents with lots of personal stuff portrayed in drama. Nevertheless it was a very good drama.
I do not believe for one minute that that man, Colin, really believes all the religious stuff he spouts. He's a psychopath. He talks the talk to try and justify what he did (no doubt he still does in prison), he brainwashed Hazel, and he gave out an aura of respectability. However there is nothing respectable in anyone's book about committing a carefully planned double murder and he and Hazel might have got away with it. I mean, "Putting them out of their misery", give me strength! If that isn't blaspheming against the Holy Spirit, I don't know what is. He is an arrogant man and has no doubt found a way to quite enjoy his prison sentence, manipulating other inmates; one would hope, not the staff.
It was a good insight into how 'religious' society is in Northern Ireland compared to us. James Nesbitt hails from NI and remembered how the scandal rocked Coleraine when it all came out.
Had the pair not hailed from and lived in Northern Ireland but over here, the man would have found something other than religion to give him a respectable air and a different justifications for his actions.