Holmes explains that several clues all pointed to Joseph: the thief knew the ways of the office well, given that he had rung the bell just before seeing the treaty; Phelps had shown his relatives around the office; Joseph had dined in London that evening, and took the 11:00 PM train to Woking; Phelps expected to meet him for the train; the theft happened at about 9:40 PM; it was a rainy night, but there were no wet footprints in the passage or office, so the thief had come in a cab; and the burglar who tried to break into Phelps' room was familiar with the layout of the house and the habits of those who lived there.