The DHS and NJ law enforcement officials analyzed data on 29 mass shootings. Ackerman summarizes the findings:
The basic pattern found by the New Jersey DHS fusion center, and obtained by Public Intelligence(.PDF), is one of a killer who lashes out at his co-workers. Thirteen out of the 29 observed cases “occurred at the workplace and were conducted by either a former employee or relative of an employee,” the November report finds. His “weapon of choice” is a semiautomatic handgun, rather than the rifles that garnered so much attention after Newtown. The infamous Columbine school slaying of 1999 is the only case in which killers worked in teams: they’re almost always solo acts — and one-off affairs. In every single one of them, the killer was male, between the age of 17 and 49.
The Dish 