We describe an exercise based on the 1964 murder of Catherine Genovese--a murder observed by 38 witnesses, none of whom called the police. Students read a summary of the murder and worked in small groups to design an experiment to test the competing theories for the inaction of the witnesses (Americans' selfishness and insensitivity vs. diffusion of responsibility and pluralistic ignorance). A pretest-posttest assessment revealed a significant increase in students' ability to design experiments to test competing theories, and anonymous feedback revealed that the exercise encouraged students to appreciate the complexity of trying to explain real-world phenomena.