Well, i don't know where he his, TBH i don't have the slightest clue. But logical places to look, i would say are:
Temple of Helm (ALL of them, remember the one in the bridge district)
Radiant Heart Hall - are you sure you went everywhere inside it, and you didn't just miss him accidently?
Garren Windpsear's house in the W.P hills, he's with the radiant heart. That's all the logical places i could think to do with the radiant heart.
Also, he could be hiding at say, Desolar's inn, the law doesn't seem to be much with that place.
I'd also say search the sewers, a good palce to hide IMHO. But i doubt he's in any of those places, and you're not suposed to find him. Hope that helped. TBH i doubt it did, i don't have a clue
