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.

It would not be difficult, to take an impression of Monsieur Darzac's footprints, and have similar boots made for himself.

Such tricks were mere child's play for Larsan, or Ballmeyer.
"Receiving no reply to his letter, he determined, since Mademoiselle Stangerson would not come to him, that he would go to her.

His plan had long been formed.