Once you regain control, open the evidence tracker (aka. Detective Mode). Look to the window on the right and put the cursor on the bullet hole. Hold the A button until the green encircles the whole cursor. Once you've done that, search the floor in the center of the room for another bullet hole. Again, hold the A button. This will calculate the trajectory and your next destination.
Use the grappling hook to climb back up to the ledge the guard was originally on. Drop down the ladder and run back through the hallway. Instead of going back down the stairs, continue on through the door with the green exit light beyond. Once outside, you can use the grappling hook to get up to the flag pole and to the roof. Feel free to listen to the guys bellow for some fun banter. When done, turn left and you should see your destination. It's a large thin tower with red banners running down the length. Make your way over and you can sit on top of one of the gargoyles. Drop down on the guards, there are only three of them. Once you've dealt with them head through the big door.
