Well, if ya want to name dead thieves...
Adolpho
Bright, Willoby(cutpurse, probably dead)
Cather
Dranko
Felix
Fredrik (maybe a thief)
Graham, Morgan & Eddy
Gruliac
Marcus
Rafael
Sutter #1

"...there is a thief one can hire who lives nearby, close to de Perrin street."


Thieves of varying skills and experience:
Amanda & Zachary
Burt & unnamed fellow mine looter
Captains Carr, Davidson, E.F. Regalio, and (the dead) William "Dark" Markham (and his man Thomas)
Carter, Finn
Cavey
Davey
The Downwind Thieves' Guild leaders Donal and Reuben, and their trusted men Thom and Magrin.
Jacksweed & unnamed female pagan and Shaman Cornbriar & unnamed pagan (in Kurshok territory looking for The Crown)
Gamall
Gelland
Gerwitz (maybe a thief)
Lavinia & Watch Officer Brice (looking to steal the Nereid Telescope from Moira)
Milton & Craig (if they weren't killed by player or AI)
Osterlind, J.
Raoul (successfully steals provisions for himself, and if he could bring himself to do so, he could steal Lady Valerius's possessions, too.)
Ember and Elizabeth Rutherford (thieves, though not by profession)
Sangar (grave-robber type)
Scully (imposter Garrett)
Solus, Downwinder
Standish, Lapdog (looking to steal from Moira)
Steinkrauss (maybe a thief)
V & M (looking to steal from Moira)
Valerius, Lady, & Captain Colliard (and maybe Ian Cribs)
Verrilli, Downwinder
Weaver, Fey (unused TDS Thieves' Guild thief?)
Zhan

Skin thief. :grr:

Lupin the 3rd.

Or any of the main characters in the Grand Theft Auto Series. Car theft counts, right?