I'm of the 'go to the police' camp. Just tell them what you know, your concerns, etc. The pedo may already be on their radar and you might fill in some missing pieces of info for them - you never know.
I remember a similar situation some years ago. One JW sister, who had kept years of childhood abuse (by a JW pedo ring) secret, was so alarmed that one of the perps had remarried and had a baby daughter, she just HAD to inform the police of his past activities. The police took her very, very seriously - big investigation - ran into the JW wall of silence and reluctance to cooperate, of course. Huge unpleasant saga with an unsatisfactory result in some ways - the police believed it, but there were legal technicalities why a successful criminal court case couldn't be brought against the perps. She later won a civil case against one of them, and as for the rest of them, they are at least on record and the police file remains open.