"How do you explain that, on the night of the murder of the keeper,"
the President asked, turning to Rouletabille, "the murderer brought
back the papers stolen from Monsieur Stangerson?--How do you explain
how the murderer gained entrance into Mademoiselle Stangerson's
locked room?"

"The last question is easily answered. A man like Larsan, or
Ballmeyer, could have had made duplicate keys. As to the documents,
I think Larsan had not intended to steal them, at first. Closely
watching Mademoiselle with the purpose of preventing her marriage
with Monsieur Robert Darzac, he one day followed her and Monsieur
into the Grands Magasins de la Louvre. There he got possession of
the reticule which she lost, or left behind. In that reticule was
a key with a brass head. He did not know there was any value
attached to the key till the advertisement in the newspapers revealed
it. He then wrote to Mademoiselle, as the advertisement requested.
No doubt he asked for a meeting, making known to her that he was
also the person who had for some time pursued her with his love.
He received no answer. He went to the Post Office and ascertained
that his letter was no longer there. He had already taken complete
stock of Monsieur Darzac, and, having decided to go to any lengths
to gain Mademoiselle Stangerson, he had planned that, whatever might
happen, Monsieur Darzac, his hated rival, should be the man to be
suspected.

"I do not think that Larsan had as yet thought of murdering
Mademoiselle Stangerson; but whatever he might do, he made sure that
Monsieur Darzac should suffer for it. He was very nearly of the
same height as Monsieur Darzac and had almost the same sized feet.