"There is where you are mistaken," declared Professor Long. "The janitor, and two assistants whom he hired, cleaned out the school late Friday afternoon. I know, for I remained here to go over some of my class records. It was late when I left, and the janitor had finished before I was ready to go. I know this because Riggs asked me to be sure and close the front door and put the spring lock on when I came out. I was the last person to leave the school Friday night, and I locked the door. Riggs had gone. The reason why he did his cleaning work Friday night, and not Saturday, as is usual, was because he wanted to go away over Sunday. He did go, I understand, so you see you boys were the only ones in the school."