If collective reactions to danger have long been portrayed as antisocial and self-preservative, research has shown that prosociality is maintained and sometimes fostered in life-threatening circumstances. In this research, we interviewed 32 survivors of the attacks at ‘Le Bataclan’ (on the evening of 13-11-2015 in Paris, France) with the aims of offering a typology of social behaviors undertaken in the context of a mass shooting in a close environment, and examining the situational factors favoring the emergence of socially supportive behaviors among hostages. Consistent with previous findings, we found that socially supportive behaviors were frequently reported, and they were more common than socially unsupportive behaviors in the narratives of the respondents. We also found that the occurrence of socially supportive actions is dependent on key contextual factors, namely the impossibility to egress, increased distance and/or minimal protection from the source of danger, and emotional fusion with other crowd members. Finally, although supportive behaviors can be served by a variety of motives (individualistic, cooperative or altruistic), we found that supportive actions were more often described by respondents as reflecting genuine altruism, i.e. involving a cost to oneself at the benefit of others. Those results bring evidence of the maintenance of socially supportive actions in the context of a mass shooting. It also calls for establishing a clear-cut distinction between the social strategies (asocial, socially supportive, or socially unsupportive) and the psychological motivations underlying them (individualism, cooperation or genuine altruism) in future research.