Time trends in a study of 440 mass slayings/rampages occurring in public places

We looked for variations in the timing of mass slayings/rampages (MS/R) committed in public places by solitary perpetrators. News reports on 440 MS/R from 1920 to 1996 yielded 379 onset times which were examined for temporal patterns. There was a dramatic increase in the number of MS/R from 1966 to 1995. We observed a significant monthly variation with peaks in July-August and December, and a bimodal daily rhythm for MS/R onset with a major peak at 11:00 a.m. and a minor peak at 8:00 p.m. Observed time trends for MS/R could help develop protective programs to reduce stress and violence in public places.