Certainly it is in the explanation of the fact, and the reconciling of it with our general notions that we shall find most difficulty, and not in accepting for true a story which is so fully proved, and that not by one witness but by a dozen, all respectable, and with no possibility of collusion between them.
The fact of the presence of the chambermaid--who had come to clean up The Yellow Room--in the laboratory, when Monsieur Stangerson and his daughter returned from their walk, at half-past one, permits us to affirm that at half-past one the murderer was not in the chamber under the bed, unless he was in collusion with the chambermaid.