Walkthrough
First, go outside, go down the hallway, take the extinguisher, u will need it later, go into the janitors closet grab the gun,blow the head off the guy by clicking the gun in ur inventory, then click, say your prayers, go in the locker that is out of ordinary, get the green box, go back to the hallway where you got the fire extinguisher, go into that classroom shoot anything Alcud, throws at you, after u shoot 3 things out of the air, shoot him while hes confused, take the key, exit the room, go back to the locked area, use the key to get into the girls room, just keep clicking on the trail of red as he moves to kill him, u cannot dodge his slashes, once he is dead, go to the end of the school, go into the teachers lounge, go back to the first room you were in, use the night vision goggles to get the key, go BACK to the teachers lounge and to kill Casandra, shoot her eyes to stop those blasts, and shoot the big tank of flammable liquid on her left side to kill her faster, shoot the barrels and the chunks of ceiling that come at you and keep shooting her crotch until she is dead!
Hope this was helpful!
-Sean