I think you are entirely colorectal in what you chose as a dark episode. It was particularly grizzly when he smiles as his dogs tear apart his erstwhile friend. Also loved seeing a very young Kim Cattrel in that episode.
I agree with you completely. There is not a thing to like about the two murderers you mentioned. In some other episodes the murders have a 'decent side' but not those two. Credit to the actors and writers for creating such dark characters.
I feel funny bringing it up this week for the obvious reason, but there's another very dark moment in A FRIEND IN DEED. It's when Mark Halperin pretends to be desperately trying to give Margaret mouth-to-mouth, knowing she isn't alive!