Monitor mass shooting statistics with Mass Shooting Tracker.
Also look at the Gun Violence Archive, which does not include deaths due to suicide.
Mass shootings are defined by the FBI as “FOUR or more shot and/or killed in a single event [incident], at the same general time and location, not including the shooter” though definitions vary across jurisdictions and by use.
Check out this guide from The Washington Post‘s Wonkblog to see how alternate definitions change how the total number of mass shooting events is calculated.
Mass Shooting Journalism 