Head back inside and through the window you jumped through earlier. This time you should have no trouble hacking the panel. Hack it and go back down the hall and to the railing. Turn left and climb up to the vantage points. You'll see a couple of thugs harassing someone below but before you intervene, there is a new enemy type down there. It's an armored enemy type. To deal damage, you first need to hit the B button to stun them. Then attack them like any other guy. Be warned that this guy also has a knife (they really didn't want this to be easy). Despite having only three enemies, you're looking at a very varied fight so stay on your feet. They are an Armored knife thug, a knife thug, and a regular guy. Make sure you dodge when necessary and you'll be fine. I highly recommend getting the Knife counter Takedown as soon as possible because it will make dealing with the armored knife guys easier.
Just to the right of the cop is your exit. Go down the hall and through the single door. You can't do anything on either side of the hallway yet. Turn right up ahead and inspect the gate you can't seem to open. You'll be told to use a remote control baterang (control is inverted by default). You want to throw it up and over the gate then back down to hit the button. Follow the hall left and go through the door.
