Was he on medication still when he attacked, that can cause behavior issues. Actually, having just been neutered his body is adjusting to a change in his hormone levels. I think, I don't know, but maybe you could wait until he is off of any medication and has a couple of months to adjust to the change in his hormone levels.
And then put him through boot-camp. What I mean about boot camp, is get a trainer, take him classes, work with him daily, obedience commands, and make sure he is securely crated when you cannot supervise. It is up to your mom if she wants to try again to be around him. It is very possible that this incident was caused by the changes in his anatomy and with meds.
If you put the dog down, that is very sad. Understandable, but sad nonetheless. I am sorry you are going through this.
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