who passes Fuchs?
that scene when he's finnished work, he turns out the lamp and walks towards the camara, you get a strange noise while unknown person walks past in a sort of shadow? i think it's blair because you get that same soundeffect when he pushes his fingers into garry's face later on.

You mean Fuchs? The shadow passes Fuchs. I personally think it's Norris-thing assimilating Palmer due to its sheer mass. I think Blaie was infected when the lights were out.

I guess it was Palmer, don't know why.