I saw her from this window, as I was looking diagonally across the court.

She was in one of the opposite rooms over there----" The superintendent broke into a hearty laugh.
"Fooled!" he cried.

"You police detectives are a smart crowd, but our old factory with its string of useless windows has led you astray for once.
You weren't looking into any one of the rooms over there.

You were looking at a reflection in that useless old window behind which the elevator runs.

That happens when the elevator running on that side is down.