Rooftop (Chapters 2 and 3)

How can I get the object from underneath the killer stone slab?
How do I open the locked door?
I'm trapped in a room, and I can't breathe!
How do I open the door in the hangman's room?
How do I kill the gunner standing out on this level?
I've done everything in the previous hints, but I can't go anywhere!
How do I open the door that the gunman closed?
So what's next?  All I see is a plank over the street.
Checklist: Rooftop

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