The study is a mixed bag, severely flawed–it’s definition of active shooter event ASE is much broader than “mass shooting” plus, based on an earlier report it seems that ASE may includes situations where only one victim is unrelated to the shooter–but includes this:
In 5 incidents (3.1%), the shooting ended after armed individuals who were not law
enforcement personnel exchanged gunfire with the shooters. In these incidents, 3 shooters
were killed, 1 was wounded, and 1 committed suicide.
■■ The individuals involved in these shootings included a citizen with a valid firearms
permit and armed security guards at a church, an airline counter, a federally
managed museum, and a school board meeting.25
25 Player’s Bar and Grill, May 25, 2008; Tom Bradley International Terminal at Los Angeles International Airport, July 4, 2002; Youth with a Mission
Training Center/New Life Church, December 9, 2007; United States Holocaust Memorial Museum, June 10, 2009; Panama City School Board Meeting,
December 14, 2010, Shooter wounded.