The only way to keep your cat from hunting and killing other animals is to keep them inside.  The question https://pets.stackexchange.com/questions/7977 shows that putting a bell on the cat is not 100% effective.  

The cat will still hunt, the bell may or may not give the other animals sufficient notice to escape.

We have the existing question https://pets.stackexchange.com/questions/8158 with a GREAT answer by Zaralynda. that speaks to psychologically issues.  But keep in mind, bells don't make hunting a no-win situation, it just makes it harder for the cat to catch the animal.