We integrated existing cognitive processing models of posttrauma reactions into a longitudinal model. Data were obtained after a multiple shooting in a city office block. The subject group comprised 158 office workers who were in the building at the time of the shootings. The methodology of this research was a repeated measures survey, with data collection at 4, 8, and 14 months posttrauma. Measures included the Impact of Events Scale (IES) and the Symptom Checklist-90-Revised. A path analysis was performed with the IES as an indication of cognitive processing. Intrusion and avoidance were shown to mediate between exposure to trauma and symptom development. Intrusion was also found to be negatively related to subsequent symptom levels. The findings provide provisional support for a cognitive processing model.