1) He drowns turtles in the toilet
2) He drowns mice repeatedly in his water bowl;
At least they died together...
3) He is slowly trying to make everyone go insane by A) knocking over and destroying any living thing in the house, B) refuses to let me sleep a full night = sleep deprived people go crazy easier
4) He is trying to dig himself a place to hide the bodies in his litter box; No cat needs to dig for ten minutes in a litter box at 4:00 A.M. unless he is trying to hide something
5) He is suicidal
UPDATE: added evidence in the case Vegas VS the state of Massachusetts; He does not take no for an answer, and will hunt cleo mercilessly even though she has repeatedly displayed her dislike for him (I am no cat but I am pretty sure that hissing, growling, scratching, and running away means "no")