When I was 10 we had to give our cocker to the humane society. He was really sweet most of the time and I loved him, but he would get randomly aggressive and bit me twice, then bit a neighbor another time. Rescues wouldn't take him because of the bite history.
He was put down, but solely because of his aggression and unpredictability. In normal circumstances the HS there is no-kill, but they couldn't take a risk with a dog that was so unpredictable and had a history of attacking children. I understand why they did it and support it, as sad as it was.