In 2018 the Federal Bureau of Investigation released a report titled “A Study of the Pre-Attack Behavior of Active Shooters in the United States Between 2008 and 2013.”
In addition:
In July 2019 the U.S. Secret Service released its report “Mass Attacks in Public Spaces—2018”
The results were similar to those of another study published by the Secret Service on 28 such attacks in 2017.