This discussion may contain spoilers!
I know it sounds Heavy Rainish but i think it would be premature to exclude Bigby from the list of suspects.
First off, he has a lack of a definite alibi. He couldve killed Faith when we all though he was asleep in his appartment. Also there is no clear evidence that he walked directly into the trip trap when he got out of the cab with Snow. He might have taken a detour.
Also. He does have a Snow fetish, smokes Huff & Puffs, and wants Snow to replace Crane as deputy mayor which would give him motive to frame Crane.