OH NO!!
I am so sorry
This is terrible. I think you probably made the right decicion having him PTS because if the damage was that bad he probably wouldn't have been able to live a life that he deserved
It's a hard decicion but you did what was best for your baby. I am so sorry.
As for the other dog you need to report it to the aniaml control asap they need to take the dog into quarentine and you need to tell them about all the animals it has killed. This is a horrible situation but if this dog is going to continue to kill and your family is deeming this ok then you need to take action to make sure this never happenes again. I do not condone the shooting of any dog i just want to make that clear but i do believe if the animal is a killer it should be PTS.
Again i am sorry for you loss hun, we are here for support.