One of the great lessons Coquenil had learned in his long experience with mysterious crimes was to be careful of hastily rejecting any evidence because it conflicted with some preconceived theory.  It would have been easy now, for instance, to assume that this prim spinster was mistaken in declaring that she had seen the pistol thrown from the window of Number Seven.  That, of course, seemed most unlikely, since the shooting was done in Number Six, yet how account for the woman’s positiveness?  She seemed a truthful, well-meaning person, and the murderer might have gone into Number Seven after committing the crime.  It was evidently important to get as much light as possible on this point.  Hence the need of M. Gritz.

M. Herman Gritz was a short, massive man with hard, puffy eyes and thin black hair, rather curly and oily, and a rapacious nose.  He appeared (having been induced to come down by the commissary) in a richly embroidered blue-silk house garment, and his efforts at affability were obviously based on apprehension.

Coquenil began at once with questions about private room Number Seven.  We had reserved this room and what had prevented the person from occupying it?  M. Gritz replied that Number Seven had been engaged some days before by an old client, who, at the last moment, had sent a petit bleu to say that he had changed his plans and would not require the room.  The petit bleu did not arrive until after the crime was discovered, so the room remained empty.  More than that, the door was locked.

“Locked on the outside?”

“Yes.”

“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.