OMG, that's just horrible what they did.

In your state is there any rules that may have been broken with them killing the dogs that way?
God Bless you for taking the other dogs and getting them away from such horrible people that thinly disguise themselves as a rescue.
I'm sorry I don't have any advise for you. Maybe look on PetFinder to see about other rescues in your area to contact. Best Wishes and Good Luck.