Old predators will kill a human as well, merely because they can't catch their normal prey, which is too fast for them. Wounded animals will kill in self-defense.
I don't think that animals who kill humans are necessarily "off"; it may simply be, in their view, self-defense--we do tend to just take over an animal's normal habitat, then bitch when the animal "retaliates," ie, when coyotes kill livestock that is penned on what used to be their hunting grounds, when individuals venture into an animal's territory.
While I think that animals do kill with premeditation--how can you not consider killing for food premeditation, after all--I don't believe they kill with MALICE. Animals will often NOT kill when killing would be to their benefit, such as when a wolf fights for dominance. When the other wolf shows submission, the dominant wolf stops fighting. A human would press the advantage and kill. The animal is much more civilized, due to instinct, than humans tend to be with rules for behavior. That's the difference between animals and humans. Humans tend to kill for either no reason, or for inadequate reason; animals kill for a purpose: food, defense, instinctual passing on of genes. We can't apply our morals to animals. If we aren't going to treat them with the same consideration with which we treat human beings, we shouldn't expect them to adhere to our standards.
That's my story and I'm stickin' to it.
Sidhe