This study tested social cognitive theory of posttraumatic adaptation in the context of mass violence, hypothesizing that pre-event protective factors (general self-efficacy and perceived social support) would reduce posttraumatic stress symptoms (PTSS) and depression severity through boosting post-event coping self-efficacy appraisals (mediator). We qualified hypotheses by predicting that post-event social support barriers would disrupt (moderate) the health-promoting indirect effects of pre-event protective factors. With a prospective longitudinal sample, we employed path models with bootstrapping resampling to test hypotheses. Participants included 70 university students (71.4% female; 40.0% White; 34.3% Asian; 14.3% Hispanic) enrolled during a mass violence event who completed surveys one year pre-event and 5-6 months post-event. Results revealed significant large effects in predicting coping self-efficacy (mastery model, R = .34; enabling model, R = .36), PTSS (mastery model, R = .35; enabling model, R = .41), and depression severity (mastery model, R = .43; enabling model, R = .46). Overall findings supported study hypotheses, showing that at low levels of post-event social support barriers, pre-event protective factors reduced distress severity through boosting coping self-efficacy. However, as post-event social support barriers increased, the indirect, distress-reducing effects of pre-event protective factors were reduced to nonsignificance. Study implications focus on preventative and responsive intervention.