What exactly is he talking about? He says 'all the children's windows' - is he saying he was checking all the children of the group? The McCann children were all in one room with one window.
I take your point about not being about know if the window was open or closed if the shutters were down.
At his 9:00 PM check he did a outside listening check on three apartments.
I have a feeling Matt was concerned about something, so when some of the group were late he went back and checked up on them, but how far did his check go, how thorough was it? When I worked as a security guard we were taught how to check the security of a building, I can't even be sure that the McCann's front door was locked at all. No one checked it as they left by the patio door. No one like Matt who is supposedly around on that carpark side of the building says he checked the front door for security yet he says the blinds and the windows were closed.
I have a horrible feeling the McCann's front door wasn't locked.