Only the OP can judge how much they have to lose by pursuing a formal police investigation, where society can potentially gain.
But assuming he's single, lives alone and is upfront and honest about his activities to the police, they should be reasonably accommodating with regard to utmost direction as far as possible. In that case, there's little reason not at least establish contact with his local station. Perhaps someone better informed can advise with regard to how much, if any, anonymity he would be offered in giving formal evidence, assuming this did go all the way to trial. Given this scumbag's record and the fact he's very possibly still on probation however, I doubt it'd take much due process to get him back behind bars, where he clearly still belongs.
If, on the other hand, he's married, has kids or is in any sort of serious relationship, he could probably do without the grief and potential loss of these. But again, I imagine this all depends on the degree of discretion and anonymity the police is willing to offer.
But even if, after careful consideration, he decides on the latter, he should still certainly file some sort of anonymous report with Crimestoppers or the 101 service, as other posters have suggested. In his position I'd want as much vengeance with as little further personal risk as possible.