The Creepy Janitor annoyed Feeny enough to give detention to Cory, Shawn, Topanga, Angela, and Kenny, all of whom he had been angry at already. He walked into the classroom, changed the garbage, and pointed menacingly at Cory before exiting.
He appeared again once everyone was in detention. Shawn asked him for the keys, and he held them up, and then walked away. Later on, he appeared dead in the hallways in a garbage can amongst many retainers. Both of these occurred in Shawn's dream.
The janitor was a suspect in the murders of Mr. Feeny and Kenny before his demise.