People who kill people generally don't have a problem with doing it, particularly when it's premeditated.
Therefore it's probably not that surprising that Colin Howell (right) was able to keep his dark secret to himself for almost two decades.
He'd got away with the murder of his wife and the husband of his former lover, making it look as if they had gassed themselves in a suicide pact.
So, coolly, he carried on with his dentistry business, married again, had more children, was a pillar of his local community.
And if he hadn't told someone about his crime, he'd still be a free man today.
Understandably, we're fascinated by the case, by how long he held his nerve, and by what finally caused him to lose it. He had got away with it but, privately, did it haunt him every single day? Or not? What changed? On and on the chit-chat goes, as we ponder every twist and turn. As if it's a rare thing.
Yet, thousands of killings from the Troubles go unsolved.
All around us people go about their business without ever feeling the need to get it all off their chests.
I suppose we just have to keep our fingers crossed that something similar will happen to all our other killers who seem to live their lives without a flicker of conscience.