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What the deadliest mass shootings have in common

The deadliest mass shootings in recent history have had one thing in common: the perpetrator used an assault rifle.

Why it matters: These weapons possess an incredible amount of killing power, and amplify the destructive will of the person who carries out an attack. Nine people died and 27 were injured in a mass shooting in Dayton, Ohio in an attack that lasted 32 seconds. The killer used an AR-15 style assault rifle.

  • Since 1999, there have been 115 mass shootings (defined below) in which 941 people were killed and 1,431 were injured.
  • Of those 115 attacks, 32 — just over a quarter — involved semi-automatic rifles. But those attacks accounted for 40% of all deaths and 69% of all injuries.
  • Since 2017, 12 of the 31 mass shootings involved assault rifles — which caused 39% of the deaths and 92% of the injuries.
  • That includes the Las Vegas massacre — which alone accounts for almost 40% of all mass shooting injuries since 1999. The perpetrator of that shooting used over 20 assault rifles during that attack.

About the data: This chart uses Mother Jones' dataset on mass shootings, which tracks the events since 1982. Our analysis is focused on shootings since 1999 — the year Columbine took place.

  • The data classifies a mass shooting as an attack in a public place where at least 4 people are killed with a gun.
  • This benchmark was lowered to 3 in 2013, after a mandate from the Obama administration to study mass shootings. Events in the data reflect the lower benchmark after 2013.