ID: Inspect the window for any clues.

You thank the bartender for the answers and the water, heading over to the windows. None of them have anything of interest - you figure he must have been at the middle window, since that's the only one that seems to have an unlocked latch. When you walk over, though, the woman wiping down tables seems to move away from you. For the moment, you disregard that, looking a little closer at the middle window. There isn't any trace, save for some displaced dust where it looks like he put his hand.