Various. Top 5 of Anything research 2020.Data is worst massacres committed with a firearm by one person in recent, known, history that can be verified. Age is perpetrators age at the time of the killings. List does not include the perpetrator in the number of people killed. List is accurate as of June 2016.Important note: Top5ofanything.com presents this unfortunate list in the interest of historical facts only. Top5ofanything.com is completely against the exploitation of these horrible crimes for entertainment or business purposes. We are acutely aware that each victim listed above was a person with a family and friends who deeply feel their tragic and senseless loss.