Mass shootings have a strong impact on public discourse and perception, affecting more than their direct victims. We use data on charitable contributions and criminal activity in the U.S. over the last decade to identify and quantify the effect of mass shootings on prosocial and antisocial behavior. We find that the effect of mass shootings on prosocial behavior, measured primarily by monetary contributions, is positive and statistically significant. However, the directly affected localities react to mass shootings differently than their neighboring communities, decreasing their charitable contributions. Additionally, we are unable to find a statistically significant effect of mass shootings on antisocial behavior, as measured by various crime rates. Furthermore, we show that mass shootings are different than any other type of criminal behavior, including all other violent offenses, in terms of its effect on prosocial behavior.