Decisional bias (false alarm rate) when judging the guilt/innocence of a suspect is offered as an implicit measure of moral judgment. Combining two data sets, 215 participants, ages 10-12, 13-15, and 16-18 watched the visually identical film involving a person setting a fire, framed either as (a) intentional but not resulting in a fire (BI-NF), (b) unintentional but resulting in a major fire (NI-F), or (c) intentional and resulting in a major fire (BI-F). After watching the film, participants identified seriatim who of six individuals was the perpetrator and how certain they were. The data were subjected to a signal detection analysis. Participants also explicitly judged "how bad" the perpetrator and act were. The implicit measure fit Piaget’s claim of moral realism, shifting from judging wrongness according to the outcome to judging according to the actor’s intentions, better than the explicit traditional measures.