evident that one of the four present in the gallery must be a double
--he must be himself and the murderer also. Why had I not seen
this before? Simply because the phenomenon of the double personality
had not occurred before in this inquiry.

"Now who of the four persons in the gallery was both that person
and the assassin? I went over in my mind what I had seen. I had
seen at one and the same time, Monsieur Stangerson and the murderer,
Daddy Jacques and the murderer, myself and the murderer; so that
the murderer, then, could not be either Monsieur Stangerson, Daddy
Jacques, or myself. Had I seen Frederic Larsan and the murderer
at the same time?--No!--Two seconds had passed, during which I
lost sight of the murderer; for, as I have noted in my papers, he
arrived two seconds before Monsieur Stangerson, Daddy Jacques, and
myself at the meeting-point of the two galleries. That would have
given Larsan time to go through the 'off-turning' gallery, snatch
off his false beard, return, and hurry with us as if, like us, in
pursuit of the murderer. I was sure now I had got hold of the
right end in my reasoning. With Frederic Larsan was now always
associated, in my mind, the personality of the unknown of whom I
was in pursuit--the murderer, in other words.

"That revelation staggered me. I tried to regain my balance by
going over the evidences previously traced, but which had diverted
my mind and led me away from Frederic Larsan. What were these
evidences?

"1st. I had seen the unknown in Mademoiselle Stangerson's chamber.
On going to Frederic Larsan's room, I had found Larsan sound asleep.