My 5-year-old neutered Rot has killed 10 cats and other dogs; he has bit my nephew in the face. What can I do?

Hi, I have a 5 yr old neutered rottie with a strong prey drive and or dominant behavior. I had him trained when he was 2 since he was showing aggressive behavior towards people. Now he is very obedient, I can stop him from a full charge attack (on people or other animals) BUT when left alone he kills. To date he has killed about 10 cats and dogs, numerous snakes, rats, birds and he even tried to take down my horse when I first got her.

I have three kids 6,5,3 and he is absolutely great with them. He even takes commands (sit, stay, quiet) from my 3 yr old. One day, though, he severely bit my nephew who was visiting. The kids went into the dog room alone and when the baby yelled the dog bit my nephew in the face. As for other people, when I am there I can have people in my yard and he will go after them but then will sit-stay when told and leaves them alone.

As for other animals entering my yard though, can I train him to not kill? I'm afraid someone is going to bring suit against me. I think he knows its wrong. When he does it he will come to me with his head down in a submissive behavior and wants to lick me a lot. Please give me some advice as I'm not sure why such a sweet passive dog one minute can become a killer in another.

Thank you
Marisol