"Was the garden door shut?"
"It must have been, as we had to unlock it at seven o'clock."
"With what?"
"With the key on the bunch."
"But how could the murderers, coming from the outside, have opened it?"
"With false keys."
"Have you a proof which allows you to suppose that it was opened with false keys?"
"No, Monsieur le Préfet."
"Therefore, until we have proofs to the contrary, we are bound to believe that it was not opened from the outside, and that the criminal was inside the house."
"But, Monsieur le Préfet, there was no one here but Sergeant Mazeroux and myself!"