Help! Jack Russell Terrier Behavior help?

I have a ten month old male jack russell terrior, and recently he has not had well behavior. I was house sitting a friends jack russell, who is also a male but he is old. The two dogs got together and attacked, and killed my cat. I know it's in jack russell's blood and that is what they were breed to do, but I am afraid that he will go beyond just cats and bite humans, or just continue to be violent. I need advice on what I should do. Should I put him down? or get a mussel and a shock collar and train him. He is just a puppy.