Criminologist Grant Duwe has researched mass killings in the U.S. and found some surprising statistics.
"Mass murder rates and mass public shootings have been on the decline," Duwe told Here & Now. "But what we did see was an especially bad year for mass public shootings [in 2012].... The number of victims who were killed and wounded was greater than in any previous year in U.S. history."
Duwe found that 0.2 percent of all homicides that occur in the United States are mass murders, and of those mass murders, 10 percent are mass public killings, such as those in Aurora, Newtown and the Washington Navy Yard.
"I think it’s important for everyone to understand the cases that receive extensive coverage, that those aren't the only mass murders that take place within the U.S.," Duwe said. "Within a given year, there are about 30 mass murders that occur in this country."
The more common mass murder is familicide, where a male head of the household kills his partner and his children, then kills himself, Duwe said.
The perpetrators of mass murder — whether public or not — are often mentally ill, he said.
About 60 percent of those who commit mass public killings suffer from a serious mental illness, Duwe said, noting that's about six times higher than the rate of mental illness in the general population.
- Grant Duwe, director of research for the Minnesota Department of Corrections and author of the 2007 book "Mass Murder in the United States: A History."
This segment aired on September 23, 2013.