Hard Time: Deathstroke Predator: 3 Medals: Batman Arkham Origins

1st Medal. There will be a guy on the left upper level who will walk around the corner to the outside. Wait for him. Make sure you dont alert the others. 2nd Medal. Then go into the vent on the same side of the room and a guy will be in perfect position for the vent takedown. 3rd Medal. The guy standing outside will run by the window allowing you to score the third medal. However, its quite frustrating since most of the time, he will go around the other side. As the other guys converge into this area, you might be able to score this medal by dropping a stun grenade. I have seen this done around 40 seconds. It requires some luck and excellent timing.