Maybe it's something learned from television cop dramas or just our own prejudices about who we think is the likely perpetrator of heinous crimes, but it's striking that the two most notorious murder cases in Northern Ireland for some time were carried out by probably the least likely suspects.
Kenneth McConnell joins Colin Howell and Hazel Stewart in a rogues' gallery which defies the stereotypes. Police inspector, successful cosmetic dentist, attractive housewife - surely for the armchair detective, these would have been the victims of nasty murderous attacks. They already had everything - careers, respectability, a good income, influential friends, social status.
Ripe, one would have thought, for the bash over the head from a drug-crazed down-and-out or cynical housebreaker from the lower classes. But no.
Instead these three were the criminal minds, the "perps", the murderers.
Their victims unsuspecting, innocent and simply in the road.
It should be a lesson to all of us not to jump to conclusions or be fooled by a shirt and tie or gold earrings.