What would you do if you found out that a very good friend of yours was a recently convicted offender?

My next door neighbor and "friend", I found out yesterday, was convicted of molesting a 12 year old boy and is suspected in molesting another youngster. I live in a neighborhood that has a lot of small children. I want to alert the neighborhood about my neighbor, but I am afraid that he might find out that I was the one that told about him and what he might do to retailate against me, my family or my home and outdoor animals, but at the same time, I don't want any more children hurt. Any suggestions?