The spell just missed - damn the legs being hard to see. But Barty stood silently without moving, so that the disillusionment did not have movement bringing it down. The flash of light from his spell had illuminated the outsider a bit, and the hair was a lightish color. No Potter, no Black. And he knew it was a man. A white man. There were a few candidates out there, and Barty did hope to know who it was, but he had other priorities.
No one had visibly stepped out from the other side of the marble wall, but that didn't mean anything, other than that aiming was ridiculously difficult without giving himself away. Barty focused his other senses as well as that gut feeling and instinct which came after so many years. But he waited - wasting nothing, and listened for something to aim at . Oh his body was alive and alert for anything.