I'm at the same part. I've activated the platform to move, went across and then that Father Grissom comes out and helps me shoot some monsters. Then I'm stuck again. Help please!
Yah, see that hallway on the bottom left hand of the screen by the stairs? Go down there and go through the halls and rooms, climb up some stairs, flick a switch. The go back to where you took that screenshot, then jump onto the platform that you just moved. Simple