PLEASE HELP I FEEL TERRIBLE?

The Dog doesn't know any better, its in a dog's nature to hunt.... and I'm sure his first aim wasn't to murder. don't really punish the dog not hit it or hurt it in any way.... Its best to tell your friend what happed soon though... you cant keep that from him forever seeing if you don't tell, and when he does find out hes going to hate you forever... er it will seem like that.... just tell him your sorry... might as well tell the truth now and get the drama over with... then to lie and when the truth is found losing your friend ship for good over lack of trust.