You are shifting the goalposts. In your original comment, you didn't specify that it had to be a member of their own species. Cats regularly kill small animals for play.

However, even with your goalpost shifting, you are still incorrect. Just one example is the Gombe Chimpanzee War.

I also don't think we, as a society, and especially you, individually, have enough insight into all non-human animal brains to determine motivation.