Was Houser, who then committed suicide, inspired by the media coverage of the earlier crime?
“I think that, unfortunately, we’ll never know exactly what he was thinking,” says Sherry Towers, a research professor at the Simon A. Levin Mathematical, Computation, and Modeling Sciences Center at Arizona State University.
Towers has determined, however, that mass killings and school shootings are contagious.
For an average of 13 days after a shooting with four or more victims, the probability that another shooting will occur is heightened, Towers argues in a new paper published in the journal PLOS ONE. About 20 to 30 percent of mass killings happen during these infectious periods.
In general, violent crime in the United States is on the decline. But, according to a recent FBI analysis, the number of shooters aiming to kill a large number of people in a public space has increased in recent years. On average, a mass shooting occurs approximately every two weeks.
Towers decided to look into the issue after a student shot and stabbed someone in the Purdue University cafeteria while she was on campus for a meeting, she says. It was the third school shooting to make the news in a week.
For an average of 13 days after a shooting with four or more victims, the probability that another shooting will occur is heightened.
“I wondered: Could that be more than a coincidence?” she says.
Previous studies have found that media reports of suicides appear to increase the incidence of suicide by planting the “seeds of ideation in at-risk individuals,” she says.
Towers estimates that mass shootings spread for similar reasons.
“The motivations of a run-of-the-mill criminal are different from the type of person who goes into a public place to shoot as many people as possible,” Towers said. “Clearly, mental health is a factor.”
In an attempt to curb the spread of suicide, the Society of Professional Journalists, in its ethics code, instructs news outlets to “be cautious about reporting suicides that do not involve a public person or a public place.”
Towers doesn’t endorse muzzling the media. But, she says, her research should be a point of ethical consideration.
“I’m not sure what the solution is,” she says. “One the one hand, I’m sure people would like to know if there has been a mass shooting in the area. On the other hand, there is this danger that people who are vulnerable might get an idea to do something terrible.”
Media coverage is just one of many factors behind the country’s mass-shooting problems, she says.
Her analysis also found a significant correlation between higher per capita rates of gun ownership and higher per capita rates of mass shootings.
“This is complex,” she said. “It’s going to require a lot more study.”