This is actually quite a simple one, no offense.
Bust open the walls, take out any enemies etc. etc. Bust open the chests on the elevated place, basically just pick up as much as you can before you move on. Now, with the dead body, you will notice that the water running behind the walls actually just revolves in this room, it doesn't run anywhere else. Place the dead body in the current (R1) and run and jump behind the partly closed gate, stand in the water, wait for the dead body to come, pick it up, place it on the button. this will open one of the sections of the gate that gets you out of here. then jump over the gate, run over to the other button, stand on it, then time a run through the door.
Murcie is back.