footmarks, of which I have taken the measurements, attest the fact
that the murderer made his escape that way. But then, how did he
do it, seeing that the blinds remained fastened on the inside? He
passed through them like a shadow. But what is more bewildering
than all is that it is impossible to form any idea as to how the
murderer got out of The Yellow Room, or how he got across the
laboratory to reach the vestibule! Ah, yes, Monsieur Rouletabille,
it is altogether as you said, a fine case, the key to which will
not be discovered for a long time, I hope."

"You hope, Monsieur?"

Monsieur de Marquet corrected himself.

"I do not hope so,--I think so."

"Could that window have been closed and refastened after the flight
of the assassin?" asked Rouletabille.

"That is what occurred to me for a moment; but it would imply an
accomplice or accomplices,--and I don't see--"

After a short silence he added:

"Ah--if Mademoiselle Stangerson were only well enough to-day to
be questioned!"

Rouletabille following up his thought, asked:

"And the attic?--There must be some opening to that?"