Mass gun killings and school shootings appear to be contagious and therefore breed more violent crimes, a new study finds.

Arizona State University researchers studied previous data from mass killings and cases of school shootings that indicate that these events did not take place by coincidence.

CBS News reports that the study, led by professor and statistician Sherry Towers, was based on previous research suggesting that some cases of suicide could also be contagious. This idea helped the team come up with the project.

The study, which appeared in the journal PLOS One on July 2, found that school shootings and mass killings—crimes involving more than four fatalities—could be contagious for about 13 days. It also revealed that approximately 20% to 30% of these killings were inspired by previous events that were similar in nature.

The study was based on Towers' experience. According to CNN, Towers narrated her story back in 2014, when she was on her way to Purdue University in Indiana for a meeting. When she arrived at the campus, she found out that the area was in a lockdown following reports of a shooting that left one student dead.

Towers then realized that there had been other cases of school shootings one week before that fateful event and wondered if it had something to do with a "statistical fluke" or if news media could have planted "unconscious ideation in vulnerable people" after the event.

Towers said school shootings and mass killings could attract attention when covered by the national news, and from there it could potentially inspire the same idea among other people.

"While we can never determine which particular shootings were inspired by unconscious ideation, this analysis helps us understand aspects of the complex dynamics that can underlie these events," eScienceNews quoted Towers as saying.

However, Towers did not mean that reports on killing sprees should not be covered. She only meant that reducing the emphasis on the killer's identity could help prevent more shootings.