Riddle: It was the first day of school and the science teacher was found dead in the hallway. The police rushed to the school and investigated. They had four suspects. The principal, the math teacher, and the custodian. Each of them had their own alibi. The math teacher said that he was preparing the mid-year math test. The principal said that she was preparing for the morning announcements. The custodian said that he was in the cafeteria cleaning the tables. The police arrested the murderer. Who was the murderer?
Answer: The math teacher. He said that he was preparing the mid-year math test. And it was only the first day of school.