Question:"He failed to keep a dinner engagement with me tonight. Do you mind meeting me at his place - say in half an hour?" Dr. Haledjiam agreed & he was waiting in the lobby of Philip Bates' apartment building when Stephen arrived by cab. "My uncle thought he was being followed the last few days," said Stephen. "He keeps a great deal of cash in a wall safe in his den. unfortunately, he isn't exactly secretive about it." "Did you try to reach him tonight" asked Haledjiam. "When he didn't show up for dinner, I phoned his home. I got no answer."
Leaving the elevator on the 14th floor, the two men walked rapidly to the door of Philip Bates bachelor apartment. It was unlocked. In the entrance hall burned the only light. "Better have a look in the den," Suggested Haledjiam. Stephen nodded & led the way. He paused at the door to the darkened room. "There's a floor lamp in the corner," he said, & disappeared into the darkness. An instant later the room was bathed in light. Directly behind the desk a small oval safe door was open. Stephen stood in a corner, one hand on the lamp, an expression of alarm twisting his face. He stepped back over the unmoving form of his uncle, who lay at his feet. "I-is he dead?" Haledjiam knelt beside Philip Bates. "No, a nasty blow on the head, but not fatal-lucky for you! You went to a lot of trouble to throw me off the scent. Then at the last minute you practically confessed to the crime!"
What was Stephen's mistake?