The Biden campaign is referring to shootings at Marjory Stoneman Douglas High School in Parkland, Florida; First Baptist Church in Sutherland Springs, Texas; and an outdoor concert in Las Vegas. In four years, there were 18 mass shootings that occurred in public places and that did not transpire during another crime such as robbery or selling drugs. (A “mass killing” is defined by criminologists as involving four or more fatalities, not counting the shooter.)