Billy will offer you a Grey Cardkey and now you can use that key to unlock the door downstairs. In the cabinets on your left, you can find the bullet-proof vest, the night-vision glasses, and the TNT explosive. Now don't hurry your way out into the air vent just yet! Go back to Billy with the bullet-proof vest or he won't be that lucky later on.
In Car 2, diffuse the three bombs using your microfilm picture files. After this is done, go back towards the beginning of Car 2 and climb the ladder. Go through the next door, across the heater bridge, kill the guard, and you should be at another ladder -- this is Car 1. Use the save box at the beginning of Car 1. You will then pick up the assault rifle, grenade launcher add-on, and grenade ammo (you need to make space to get this items -- dispose of your guns, but keep the cigarette case, life kits, and the disc). Go up the stairs and a control panel will appear. Read the memo in the control panel. Go to the left side of the control panel and turn the switch to detach Car 1 from the rest (this must be done to achieve Scenario A). Combine your rifle and grenade add-on to form a grenade launcher and head outside. There is a bomb in the front of the car. Memorize your cigarette case poem and diffuse the bomb. Mason will cut you off in his helicopter. Pull out your grenade launcher and shoot him until he is defeated.
i found a key(similiar than locker key & it has green chips in middle)in save box while i used gameshark 4 this game,and i checked it's says:"the church key" what that key use for?