He was not found because he was not there during that time." "But the evidences ?" "They have led us astray.

In reasoning on this mystery we must not take them to mean what they apparently mean.

Why do we conclude the murderer was there ?--Because he left his tracks in the room?
Good! But may he not have been there before the room was locked.

Nay, he must have been there before! Let us look into the matter of these traces and see if they do not point to my conclusion.
"After the publication of the article in the 'Matin' and my conversation with the examining magistrate on the journey from Paris to Epinaysur-Orge, I was certain that The Yellow Room had been hermetically sealed, so to speak, and that consequently the murderer had escaped before Mademoiselle Stangerson had gone into her chamber at midnight.
"At the time I was much puzzled.

Mademoiselle Stangerson could not have been her own murderer, since the evidences pointed to some other person.
The assassin, then, had come before.