Also:

"Has your confederacy deduced who I really am?" The words were spoken with deceptive mildness.

"Yes, in fact. Now -"

Pure magic, pure power crashed into the room like a flash of lightning, like a thunderclap echoing about her ears that deafened her other senses, the papers on her desk blown aside not by any conjured wind but by the sheer raw force of arcane might.

Then the power subsided, leaving only Hermione Granger's death certificates drifting down through the air to the floor.

"I am David Monroe, who fought Voldemort," the man said, still in mild tones. "Heed my words. The boy cannot be allowed to continue in this state of mind.

Though we don't know for sure what McGonagal and the rest of the "confederacy" really believes.