The first guard on patrol may just be walking past the elevator as you exit. No, don't use the elevator as exit on Big Con Gruppe6, just sneak up the stairs.
I would use the lift, it’s harder to avoid the patrols. Also if your not quick enough the camera half way up may spot you. Im fairly certain if you don’t use the stealth key to move up the stairs, the patrolling guard may hear your footsteps. I assumed the OP meant they were also spotted by a guard? Perhaps clarify?
