| FraserRonald |
I will confess that I don't play a lot of videogames, other than the Civiliaztion series, so I had to Wikipedia "Thief." From what the wiki tells me, it sounds like this is something Sword Noir could do. There might be other systems that could do it better, but the setting is not that far off from Sword Noir's setting of Everthorn.
Sword Noir's task resolution system is pretty abstract, so it can handle a lot of situations generally outside its wheelhouse, but if you are looking for a crunchier, more simulationist style, Sword Noir probably won't be able to scratch that itch.
You can have a look at the free Sword's Edge System at RPG Now or Drive Thru RPG, and that's a more basic, generic version of Sword Noir. If that works for you, Sword Noir should do the job as well.