Tragically, more than 20 percent of mass shootings, as tracked by the National Institute of Justice for the past 50 years, have occurred in the past five. The past three have been the deadliest. In the U.S., there is well-deserved attention on the availability of guns (because the deadliness of method and ease of access to weapons matter greatly) and on whether we pay sufficient attention to mental health support for troubled young men.