"Arsene Lupin doesn't leave traces all over the place.

There's nothing but traces.

Are we going to have that silly Lupin joke all over again ?" "I think, sir, that this time joke is the word, for this is a burglary pure and simple," said the inspector.
"Yes, it's plain as daylight," said M.Formery "The burglars came in by this window, and they went out by it." He crossed the room to a tall safe which stood before the unused door.
The safe was covered with velvet, and velvet curtains hung before its door.

He drew the curtains, and tried the handle of the door of the safe.

It did not turn; the safe was locked.
"As far as I can see, they haven't touched this," said M.Formery.
"Thank goodness for that," said the Duke.