"Johann, are there any more keys for the outer door?"

"Yes, sir. One more, that is, for the third was lost some months
ago. The Professor's own key ought to be in the drawer of the
little table beside the bed."

"Will you please look for it, Muller?"

Muller went into the bedroom and soon returned with the key, which
he handed to the commissioner. The detective had found something
else in the little table drawer - a tortoise-shell hairpin, which
he had carefully hidden in his own pocket before rejoining the
others.

Horn turned to the servant again. "How many times have you been
out of the apartment since last night?"

"Once only, sir, to go to the police station to fetch you."

"And you locked the door behind you?"

"Why, yes, sir. You saw that I had to turn the key twice to let
you in."

Horn and Muller both looked the young man over very carefully. He
seemed perfectly innocent, and their suspicion that he might have
turned the key in pretense only, soon vanished. It would have been
a foolish suspicion anyway. If he were in league with the murderer,
he could have let the latter escape with much more safety during the
night. Horn let his eyes wander about the rooms again, and said