Cellular respiration, the central component of cellular metabolism, can be a difficult concept for many students to fully understand. In this interrupted, problem-based case study, students explore the purpose of cellular respiration as they play the role of medical examiner, analyzing autopsy evidence to determine the mysterious cause of death for seven people. This case is based loosely on the real-life 1982 Chicago Tylenol murders in which seven people died from cyanide poisoning, which interrupts the function of the electron transport chain (ETC). Students must examine the various components of cellular respiration and the role they play in ATP production in order to determine and understand the cause of death. The case was developed for use in an introductory biology course taken by both science majors and nonmajors. It could also be used in any course where students are learning a basic understanding of the cellular respiration pathways; however, it is not advanced enough for use in upper level courses without modification. Although this case was used in a small classroom, its format could easily be adapted for use in a larger class setting.