Here's a neatly categorized and tantalizing list of medieval urban professions, including the criminal trades.
silk-snatcher - one who steals bonnets
stewsman - probably a brothel keeper - "since the words stew and stewholder both mean a bawd, I'm guessing that a stewsman would be a brothel-keeper as well. Whether bawdry counts as a criminal activity varies at different times and places."
thimblerigger - a professional sharper who runs a thimblerig (a game in which a pea is ostensibly hidden under a thimble and players guess which thimble it is under)
eggler - an egg-merchant
Knifeman - one skilled with a knife; specifically, a soldier trained to disembowel horses
I write books. My latest is a YA science fiction novel called Homeland (it's the sequel to Little Brother). More books: Rapture of the Nerds (a novel, with Charlie Stross); With a Little Help (short stories); and The Great Big Beautiful Tomorrow (novella and nonfic). I speak all over the place and I tweet and tumble, too.