"Through the keyhole," answered Muller.

"It is scarcely possible."

"Shall we try it?"

"Yes, yes, you do it." Even the usually indifferent old chief of
police was breathing more hastily now. Muller took a roll of paper
and a small pistol out of his pocket. He unrolled the paper, which
represented the figure of a French soldier with a marked target on
the breast. The detective pinned the paper on the back of the chair
in which Professor Fellner had been seated when he met his death.

"But the key was in the hole," objected Bauer suddenly.

"Yes, but it was turned so that the lower part of the hole was free.
Johann saw the light streaming through and could look into the room.
If the murderer put the barrel of his pistol to this open part of
the keyhole, the bullet would have to strike exactly where the dead
man sat. There would be no need to take any particular aim."
Muller gazed into space like a seer before whose mental eye a vision
has arisen, and continued in level tones: "Fellner had refused the
duel and the murderer was crazed by his desire for revenge. He came
here to the house, he must have known just how to enter the place,
how to reach the rooms, and he must have known also, that the
Professor, coward as he was - "

"Coward? Is a man a coward when he refuses to stand up to a maniac?"
interrupted Bauer.