The death tolls change, the places change: 26 at a church, 26 in an elementary school, 49 in a nightclub, 58 at a country music festival. The faces in the memorial photos change every time.

But the weapons are the common denominator.

Mass killings in the United States are most often carried out with guns, usually handguns, most of them obtained legally.

There is no universally accepted definition of a mass shooting, and different organizations use different criteria. In this piece we use a narrow definition and look only at the deadliest mass shootings, beginning Aug. 1, 1966, when ex-Marine sniper Charles Whitman killed his wife and mother, then climbed a 27-story tower at the University of Texas and killed 14 more people before police shot him to death. The numbers here refer to 146 events in which four or more people were killed by a lone shooter (or two shooters in three cases). An average of eight people died during each event, often including the shooters.

[The number of ‘mass shootings’ in the U.S. depends on how you count]

This data — compiled from Mother Jones; Grant Duwe, author of “Mass Murder in the United States: A History,” and Washington Post research — does not include gang killings, shootings that began as other crimes such as robberies, and killings that involved only the shooter’s family.

1,048 victims

Each gun was used to kill an average of four people, not counting shooters. The 1,048 people came from nearly every imaginable race, religion and socioeconomic background, and 161 were children or teenagers.

Hover to read each victim's story