I need advice on what to do about a stalker!?

When I was younger i started seeing an older man. I realized it was stupid n tried to cut it off. He didn't accept it. He went crazy! After this I met a man my age and got pregnant. He found out went crazy and set me up. Me and my son was kidnapped. The police wouldn't do anything because it turned out that the name he gave me was fake. After this I was afraid so I stayed at my moms a very long time. He disappeared finally and then I moved out into my first place. He showed back up one day and the next thing I knew someone broke into my home stole everything and set it on fire. After this my parents had gl bottles with gas in them thrown at their house. This cont. for a while he finally disappeared again! i finally thought I could breath then once again he showed back up at my job. The security personal said he couldn't do anything because he wasn't doing anything wrong. I am a single mom of two kids and I live alone. I am scared to death. I did research and found out he was a offender who didn't register. He is very smart and careful not to step out of bounds. What should I do? The police can't do anything because he hasn't committed a crime yet but I am scared he will hurt me or kidnap my kids. What should I do? help!