Mac Is a Serial Killer

S3 E10: Mac's unusual behavior leads Frank, Dennis, and Dee to suspect that he's the serial killer on the loose in Philly. They devise a plan to catch Mac in the act, while Charlie utilizes the vast legal knowledge he's learned from TV shows to prove Mac's innocence. When the gang learns the true reasons for Mac's mysterious behavior, they are even more sickened and horrified by their friend's behavior.