Is it okay to get my 7 year old son a pet cat?

We got him some rabbits two years ago and he killed them. Do you think enough time has passed for him to get another pet? He's requesting a cat. We think it might help with his behavioral issues. He's got a lot of anger issues and throws tantrums and threatens me a lot, we think it might get nickled in the buck if he has an animal companion to take care of to help him learn to be more polite and caring.