More or less the first 20 minutes.
It was a mindfuck to me to figure out what was going on after you smashed the window in your "apartment".
Oh and here's an important detail: sometimes you'll find people still alive but under mind control. If they see you they'll charge and explode at you. If you want to save their lives you have 3 option:
1) Find and kill the Telepath controlling them. Not easy because these suckers love to run away and have an AOE attack that can kill their mind controlled minions if they get hit too.
2) Use the disruptor gun. Simple and straightforward, however in my game I met my first mind controled guy in the Lobby before I found the gun. He was locked in a room in the medical room though so I kept him there until a found it.
3) Use the Mindjack Typhon mod. Obviously this is not an option if you're going for the "human mod only" or "no mod" playthrough achievements, but if you don't care then no problem. Oh but you need to scan a Telepath to unlock the power to begin with so…