The string of mass shootings over the past three months was one of the worst on record according to the Violence Project, a mass-shooting database run by two criminology professors. There were five attacks in which four or more people were killed in public places from March through May, matching the highest three-month total going back to 1966. Law enforcement and homeland security officials and experts theorize some of the factors behind the recent spate include increased public gatherings as COVID-19-related restrictions have eased, the stress of the pandemic on mental health, and record gun sales. “We’ve got people that have been sitting around for over a year with nothing but time to plan; all they need is that point that pushes them over toward violence,” said Mike Sena, director of the Northern California Regional Intelligence Center. Researchers also 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 probability that another would occur. Read more at the Wall Street Journal.