A string of mass shootings over the past three months, in which there were five attacks where four or more people were killed in public places from March through May, matching the highest three-month total going back to 1966, was one of the worst on record, reports the Wall Street Journal. For almost exactly a year, as the pandemic gripped the country, there were no shootings that killed four or more people in public places, according to the Violence Project, a mass-shooting database run by two criminology professors. Law-enforcement officials and threat-assessment professionals say possible factors behind the recent spate of mass shootings include the burst in public gatherings as the COVID-19 threat has eased, the stress of the pandemic on Americans’ mental health and record sales of guns last year.
Researchers theorize that some attackers are inspired by others, which could help explain clusters like the ones seen in recent months. In 2015, data scientist Sherry Towers found that in the 13 days after a mass shooting there was a temporary increase in the probability that another would occur. Towers argued that this contagion effect could be similar to ones that have developed around suicides. No evidence has emerged yet that the recent attacks were inspired by one another, but authorities say the 21-year-old supermarket shooter in Boulder, Colo. purchased his AR-15 pistol on March 16, the same day as the Atlanta spa shooting.