Therefore the murderers had not gone before eleven.

No; the gate was open for them to go, but they had not gone.

Else why should the gate again be open at midnight ?" Besnard nodded in assent, and suddenly Perrichet started forward, with his eyes full of horror.
"Then, when I first closed the gate," he cried, "and came into the garden and up to the house they were here--in that room?
Oh, my God!" He stared at the window, with his mouth open.
"I am afraid, my friend, that is so," said Hanaud gravely.
"But I knocked upon the wooden door, I tried the bolts; and they were within--in the darkness within, holding their breath not three yards from me." He stood transfixed.
"That we shall see," said Hanaud.
He stepped in Perrichet's footsteps to the sill of the room.

He examined the green wooden doors which opened outwards, and the glass doors which opened inwards, taking a magnifying-glass from his pocket.
He called Besnard to his side.
"See!" he said, pointing to the woodwork.
"Finger-marks!" asked Besnard eagerly.
"Yes; of hands in gloves," returned Hanaud.

"We shall learn nothing from these marks except that the assassins knew their trade." Then he stooped down to the sill, where some traces of steps were visible.