My own hunch is that BB is clueless as to the identity of the perp (as is his mother and the rest of the family - KS so much as admitted it in her last interview with the press). But (IMHO) BB's comments re forgiveness were rooted in his faith, and are in keeping with his historic willingness to say what's on his mind about the case whenever the opportunity presents itself.
On the other hand, I believe LE might well have a good idea as to who the perp(s) are, though not enough evidence gathered yet for an arrest. If BB is in constant touch with LE, they may even have communicated to him that this public appeal and offering of forgiveness might help the perp to come forward. (Much like the 'gentle' appeal in an earlier presser.) And whether or not you think it would have any effect on the perp(s) has a lot to do with who you think they might be (eg. jealous lover, hardened hit man, teenager, etc.).