Murder is as Easy as ABC: Ed Lazenby mystery

When Ed Lazenby let his friends talk him into being a volunteer tutor at a local middle school, he figured it would be boring, but easy, and it was only for a couple of hours, three days a week. It's not as if he had anything more important to do, anyway. But, when the school principal is found stabbed to death in his office, by Ed of all people, life becomes anything but simple. There's no shortage of suspects, but Ed has to find out how the killer got into the school with the weapon, and out again without being seen. His motives are personal; on the one hand, he's an amateur sleuth who can't resist sticking his nose into a crime, and the other-he's one of the suspects. He knows he's innocent, but can he find the real killer before a couple of overzealous detectives decide he's their man?