I'm playing a thief (among other characters) right now, and I'm trying to figure out how to get the Heron's Device and gun plans from Bates' Factory without getting caught and having to fight through all the guards. Is there a way? I went through the sewers but didn't find much... I just don't want to have to wait till I'm able to actually fight them!
Leave your party outside, use your sneak ability. Or, you can time the guards rounds and get in and out before they come back, it's very difficult but possible.
If you sneak & pick locks, they both are doable. Pickpocket, Vergil's lockpicking, & a lot of saves will get you through the Herron Device, or Pickpocket & Unlocking Cantrip. The Bates warehouse can be done on lockpicking & timing. Or Unlocking Cantrip & timing.
I always went in the daylight and used timing with that guard, but one time I started a game and was getting that artwork I noticed the guard not there..............duh! From then on I went in at night. Parmanian