~ Frame 2000 seems likely it could be sound, though in wireframe it looks as if he is actually see's him and waits for him to come up the stairs.(I have camped a few seconds there at times for kills). If he is walling he is TERRIBLE at pre-firing.
~ Frame 17200 seems even more questionable but not concrete.
Again, if he is walling, he is pretty damn terrible at it or very good at hiding it.
Also, I only watched Demo 1 as you said it was the most apparent.
Also, use
http://megashares.com/ . Having to wait 45 seconds to DL really F'ing sucks.
The crackhouse thing is pretty damn suspicious even if it was a fluke. If this is overturned, I'd keep a better eye out.
Demo 1 doesn't show it for me, will look at more later.