Weyland the Smith did it
He rapes a princess and commits other grusome acts in the comics...he is in fact the murderer.
Yes, he did those things in the old days, before the amnesty.To answer your question, no, he is not the murderer.
No, "Mr. Smith" was just a fake name that was used most likely because it's a common last name. Weyland stays up at the farm, as far as we know. He's busy running things there and probably wouldn't be able to get to the city.
A lot of the Fables have bloody, dark pasts. Obviously there's Bigby, but there's also Bluebeard, Frau Totenkinder, and several others that it would spoil the comic for me to go into. That's why they have the whole amnesty thing.
This theory should go down the drain for such a wild and unprepared thread.