Common traits like childhood trauma, behavioral changes link mass shooters
The Violence Project has studied every U.S. mass shooting since 1966. Its database, which is not publicly available yet, includes 160 mass shooters who have killed four or more people in a public place. Nearly all were male and the average age was 34-years-old. The study found most shooters shared common traits, like experiencing childhood trauma. The researchers also learned these shootings are "socially contagious." Psychologist Jillian Peterson, co-founder of The Violence Project, joins "CBS This Morning" to discuss the findings.