By the time the nation confronted the unthinkable school massacre in Connecticut last December, Mother Jones’ groundbreaking investigation of mass shootings, launched the prior summer, had shown that mass gun violence in America was on the rise. The trend appeared to be no coincidence in light of the proliferation of guns and looser gun laws nationwide. One leading criminologist took issue with our criteria, arguing that mass shootings had not become more common. But now, research from an expert on criminal justice at Texas State University further shows that gun rampages in the United States have escalated.

The research, to be published in a book in July, further confirms that:

Public shooting rampages have spiked in particular over the last few years

Many of the attackers were heavily armed

None of the shootings was stopped by an ordinary citizen using a gun

The author of the study, Pete Blair, advises law enforcement officials and has conducted extensive research on gun rampages in workplaces, schools, and other public locations. He gathered data on 84 “active shooter events” (ASEs) between 2000 and 2010 in which the killer’s primary motive appeared to be mass murder. This chart shows his findings on the frequency of cases:

More: New Research Confirms Gun Rampages Are Rising—and Armed Civilians Don’t Stop Them

The Chart does not include Newtown and many other recent mass shootings