Report: Mass public shootings on rise

Mass public shootings have increased in frequency from 1.1 a year to 4.5 a year since the 1970s, according to a new report by the Congressional Research Service.

The report, sent to members of Congress on Friday, found that in the 1970s, mass public shootings killed roughly six people a year and injured two. From 2010 to 2013, there were an average of 33 deaths in mass shootings each year, with 28 additional people injured.

The figures come after a particularly grisly July, when five mass killings — including a public shooting at a Chattanooga, Tenn,  military office that killed five service members — occurred in a span of eight days.

Mass killings are defined as singular or events with at least four victims who die within a short period of time. In mass public shootings, all the victims are killed with firearms in a public location such as a workplace, house of worship, school or restaurant.

The research found that a dozen mass public shootings since 1970 have had double-digit death tolls. Seven of those have occurred since 2007.

A criminologist who studies mass killings called the report the "most comprehensive" look at the issue in the past 15 years. “It deserves our attention,” said Grant Duwe, a Minnesota criminologist whose own research provided one source of data for the study. "Hopefully their report if nothing else will foster a more honest dialogue about the patterns and prevalence about mass shootings."

Using FBI figures, Duwe's data on mass shootings and an ongoing project at USA TODAY that tracks mass killings, the CRS researchers found that in the 15-year period between 1999 and 2013, there were 317 mass shootings with 1,554 victims. USA TODAY has counted an additional 29 mass shootings since then, with an additional 143 victims.

Among the report's findings:

• On average, 4.4 mass killings a year between 1999 and 2013 could be defined as mass public shootings. 
• Nearly double that number each year could be classified as familicides — the killings of family members or domestic partners in private places such as the home.
• Of the mass public shootings, the assailant carried a single firearm in more than half the cases. In a quarter of them, an assault weapon was used.
• Only 20 of the 68 offenders in mass public shootings were arrested. The majority killed themselves or were killed by police. 

A flurry of statistics, gun control proposals and rhetoric often come out in the aftermath of the large-scale homicides, particularly public shootings such as the 2012 elementary school shooting in Newtown, Conn., and the June killing of nine people at a Charleston, S.C. church.

The report says, however, that federal data is lacking to help guide a public policy conversation. USA TODAY's "Behind the Bloodshed" project, which has tracked mass killings from 2006 to the present, found that the FBI's homicide data on mass killings had an accuracy rate of only 57%, with many major events missing and others mistakenly included through problems with miscoding or counting injured victims among the dead.

"With improved data, policymakers would arguably have additional vantage points from which to asses the legislative proposals that are inevitably made in the wake of these tragedies," the report says.

The report suggests that Congress direct a federal law-enforcement agency to improve the collection of data on multiple-victim homicides, and that it instruct the Bureau of Alcohol, Tobacco, Firearms and Explosives to annually report on mass shootings, including data on how the suspect acquired the weapon, the victim-offender relationship, and offenders' histories of mental illness and domestic violence.

CRS researchers are non-partisan and don't comment publicly on published reports.