Mass Killings Not So Rare or Always Gun-Related, Study Finds

Mass killings occur in the United States every two weeks on average, according to a new USA Today study. The incidents stretched over a wide variety of crimes, from robberies to shooting sprees like the one that killed 27 last Friday in Newtown, Conn.

Because they involved killings of four or more people, 156 incidents across the five years studied were found to meet the FBI criteria for mass killings. In total, 774 people were killed in the attacks, including 161 young children, according to USA Today. Despite those numbers, mass killings accounted for just 1 percent of Americans murdered over the study period.

The publication took data from news reports and FBI records between 2006 and 2010, so it didn't include last Friday's tragedy in Connecticut, the shooting in an Aurora, Colo., movie theater that left 12 dead, or the Wisconsin shooting at a Sikh temple that left six dead. It is not certain if killings increased on average over the last two years, as the data was not yet available.

The report showed that a gunman acting alone, as in the three recent incidents, occurs in less than half of mass killings. Notably, a third of killings didn't involve guns at all. In 15 incidents, the victims died in fire.

Over the five-year period studied, more people died from migraines and falling out of chairs than did at the hands of mass killers, according to the U.S. Centers for Disease Control and Prevention. Three times as many people died from sunstroke, according to USA Today.

"Everybody is surprised when they hear it's dozens a year," James Alan Fox, a criminologist who has mass murders at Northwestern University told the publication. “People don't understand them. When they think of mass murders, they only think it's random."