Howard Barton Unruh was an American mass murderer who shot and killed thirteen people during a twelve-minute walk through his neighborhood in Camden, New Jersey, on September 6, 1949 in an incident that became known as the Walk of Death. Unruh was found criminally insane and died in 2009 after a lengthy illness at the age of 88 following 60 years of confinement.

Mass shootings are incidents involving multiple victims of firearm related violence. Definitions vary, with no single, broadly accepted definition. One definition is an act of public firearm violence—excluding gang killings, domestic violence, or terrorist acts sponsored by an organization—in which a shooter kills at least four victims. Using this definition, a 2016 study found that nearly one-third of the world's public mass shootings between 1966 and 2012 occurred in the United States, In 2017 The New York Times recorded the same total of mass shootings for that span of years. A 2023 report published in JAMA covering 2014 to 2022, found there had been 4,011 mass shootings in the US, most frequent around the southeastern U.S. and Illinois. This was true for mass shootings that were crime-violence, social-violence, and domestic violence-related. The highest rate was found in the District of Columbia, followed by Louisiana and Illinois.