On November 23, 2020, a fifteen-year-old boy was gunned down by five Oklahoma City police officers, after he exited a convenience store and dropped the gun that he and a sixteen-year-old partner had earlier used to rob the store’s owner. Initially, the boy’s non-present partner was charged with first-degree (felony) murder for this killing. But after months of efforts by the boy’s mother and local activists, the district attorney also charged five officers with first-degree manslaughter for this same killing. This case raises the question of whether Oklahoma—or any American state—can convict a defendant of felony murder based upon a killing that was a criminal homicide by a police officer. More broadly, it raises the question of whether a felony “participant” can be convicted of felony murder based upon a killing by a “nonparticipant,” who killed while resisting the underlying felony. Killings by “nonparticipants” include killings by responding police officers, as well as by bystanders and victims of the original felony. This is the first Article to address felony murder liability for homicides by nonparticipants. This Article presents a fifty-state survey of American law that determines which states maintain a traditional approach to felony murder (not requiring any culpable mens rea regarding a killing arising from a covered felony), which states are “agency states” (that limit felony murder to killings by participants), which are “proximate cause states” (that allow felony murder convictions for killings by nonparticipants), and which proximate cause states would potentially allow felony murder liability for a criminal homicide by a police officer, bystander, or victim. This Article maintains that even states that have adopted a broad proximate cause approach to felony murder should prevent such liability for killings by nonparticipants that are chargeable homicides and proposes some statutory and doctrinal approaches for doing so in a principled way.