The suspected gunman who killed 11 people and wounded nine more in a mass shooting at a ballroom dance studio in Monterey Park, Calif., was identified by local authorities as 72-year-old Huu Can Tran. Less than 48 hours later, a 66-year-old suspect, Chunli Zhao, allegedly killed seven people in Half Moon Bay, Calif.
That older age is uncommon.
Ninety-eight percent of mass shooters are male, and the average age is around 30, Jillian Peterson, a co-founder of the Violence Project, which maintains a national database of mass shootings, told Yahoo News. “We see two clusters: young perpetrators in K through 12 school shootings [ages ranging from 15 to 25]. We see a second cluster of mid-40s,” Peterson explained. “So the 72-year-old perpetrator is definitely an outlier. ... He’s the oldest in our database.”
Peterson, who is also a criminal justice professor and director of the Forensic Psychology Program at Hamline University in St. Paul, Minn., explained some of the reasons behind mass shooting age trends in the U.S. (Some responses have been edited for length and clarity.)
Yahoo News: How does the Violence Project define a mass shooting?
Jillian Peterson: We use a pretty conservative definition in our database: four or more people killed in a public space, not shooting family members, and not in the course of another felony, so not related to something like gangs, drugs or a robbery gone bad. The definition isolates that perpetrator coming into a place and shooting indiscriminately.
What are some of the differences between younger and older mass shooters?
The older shooters tend to be workplace shooters. You have people who got fired or suspended from their job who commit a shooting at their workplace — also at some kinds of retail restaurants.
Younger shooters, like we've seen recently, are more hate-driven, fame-seeking shootings, something that they want to go viral. School shooters and college shooters who target their own institutions are in that category as well. You tend to see more copycat features, more time on social media studying other perpetrators.
Are there any trends in terms of targeted locations?
School shootings stay pretty consistent over time. We're actually seeing fewer workplace shootings. The biggest increase lately is in retail mass shootings. More of these spaces like restaurants, retail establishments and dance clubs, where it’s not that the person is necessarily a part of that community, like schools or workplaces, but they're coming in as an outsider.
While there is no easy explanation for why mass shooters tend to be younger males, what are some of the noticeable trends?
Over 90% of all murders are committed by men — from biology, sociology, socialization, there are so many reasons. I think for mass shootings, a couple of things: Perpetrators copy and study each other. We interviewed perpetrators who literally said, “I saw myself in these previous shooters and identified with them.” So I think that’s why you tend to see these similar profiles emerging again and again.
I think sometimes there’s this sort of entitlement that comes with masculinity, like, “This is what I'm owed in this world and I’m not getting it. So I’m angry, and it must be somebody else’s fault.”
We do see common patterns. We see histories of early childhood trauma, perpetrators hitting a crisis point where they start acting differently and people around them are noticing them. Many perpetrators leak their plans ahead of time and tell other people they’re planning it. Often they’re suicidal and they pick a target that represents their grievance with the world.
It’s hard to know in the Monterey Park mass killing how that’s all going to play out because it’s still early. Having studied hundreds of these cases, I’d be surprised if there weren’t warning signs. There always are.