"With the key in the lock?"
"Yes."
"Then anyone coming along the corridor might have turned the key and entered Number Seven?"
"It is possible," admitted M. Gritz, "but very improbable. The room was dark, and an ordinary person seeing a door locked and a room dark——"
"We are not talking about an ordinary person," retorted the detective, "we are talking about a murderer. Come, we must look into this," and he led the way down the corridor, nodding to the policeman outside Number Six and stopping at the next door, the last in the line, the door to Number Seven.
"You know I haven't been in there yet." He glanced toward the adjoining room of the tragedy, then, turning the key in Number Seven, he tried to open the door.
"Hello! It's locked on the inside, too!"
"Tiens! You're right," said Gritz, and he rumpled his scanty locks in perplexity.
"Some one has been inside, some one may be inside now."
The proprietor shook his head and, rather reluctantly, went on to explain that Number Seven was different from the other private rooms in this, that it had a separate exit with separate stairs leading to an alleyway between the hotel and a wall surrounding it. A few habitues knew of this exit and used it occasionally for greater privacy. The alleyway led to a gate in the wall opening on the Rue Marboeuf, so a particularly discreet couple, let us say, could drive up to this gate, pass through the alleyway, and then, by the private stairs, enter Number Seven without being seen by anyone, assuming, of course, that they had a key to the alleyway door. And they could leave the restaurant in the same unobserved manner.