Honestly? There really is nothing you can do; if he's a registered sex offender, then hopefully adequate notification has already been provided to the community; if not, let's say you warn the guy's neighbors, and he gets wind of it- then it legally amounts to hearsay, and could result in all sorts of nasty legal problems for you, including harassment, defamation of character, etc. I don't mean to bring you down, god only knows i'd love to see my 2nd perp rot in jail (if he's still alive), but the legal system is really only useful after a crime has already been commited, and even then the burden of proof is on the prosecution. It's almost useless when it comes to prevention of SA, if the perp's never been caught, and as you've said the statute of limitations has run out. Again, even if you only "spread the word" about the creep, and it's traced back to you, the law would be on the side of the perp. I'm no lawyer, but i would urge extreme caution and self-restraint; it seems that cases where the SA happened years ago that have been resolved in favor of the plaintiff(s) have mostly involved institutions (such as the Catholic Church, etc.) where there were initial complaints, multiple victims/witnesses, and documentable paper trails/organized cover-ups. If your situation involves a lone individual, i'm afraid there's not much legal recourse, and of course i'd never recommend going outside the system, since it would only most likely backfire badly. The best i can tell you is to use all available methods to deal with your anger and frustration, and i encourage you and the survivor in your life to make the most out of resources such as this site.
I'm sorry you are in the situation you're in, but feel free to post and participate as much as you need to here, there's a lot of great people here.
Give sorrow words: the grief that does not speak
Whispers the o'er-fraught heart and bids it break.
-William Shakespeare, Macbeth, Act IV, Sc. III