Op, before i get really livid from reading your posting history, i'm going to say this. If you did NOT report each and every incident this man has put his children in danger, it is YOUR fault there is no evidence. YOUR fault!
You're right. Every time I called the police, they refused to make a report. All I can say is that when you're in the middle of that situation, having authorities tell you, while you are emotional and upset and frazzled, that they will do nothing makes the whole thing seem very hopeless. If you've never been in that situation, I would really hesitate to cast judgement. I would have been in your shoes a few years ago until I went through it myself.