He bought all of his weapons within the law. We cannot test for all types of sociopath behavior. The man's father being a bank robber though should have been enough. Police knew about him and ignored him. I don't see how they could have done anything though to prevent it. If he didn't use guns, he would have made a bomb. No bomb? He could have flown a plane into a building. Predators do not think like we do. They are sick. Laws will never stop them either. Bullets do however.