Violent media consumption is often thought to lead to more aggression and violence, especially in juveniles. Social cognitive theories assume a pivotal role for cognitive functions, such as normative beliefs, in the explanation of human behaviour (including violence) and see violent media as a possible and potent learning environment. Although many studies have analysed the relationship between violent media consumption and violence, only a few are longitudinal and apparently no study has analysed mediator effects of violence-approving normative beliefs with data from a Western country at more than two points in time. Some researchers assume that violent media consumption can only aggravate an already existing disposition for violence due to other experiences such as parental maltreatment (double-dose or intensifier effect, which is methodologically described as a moderator effect). Both assumptions – mediation and moderation – are tested with structural equation models using cross-sectional and longitudinal data from a German panel study. Results show that interaction effects between parental behaviour and violent media consumption are surprisingly weak, whereas both influence the approval of violence to a remarkable extent and mediated by this eventually, to a smaller extent, violent behaviour.