USATODAY

The 934 deaths account for less than 1%25 of all gun-related homicides

NRA says it will target any lawmaker who votes to expand background checks

Momentum for action has increased since Newtown%2C Conn.%2C shootings in December

More than 900 people died in mass shootings during the past seven years, and a majority of them were killed by people they knew, according to a USA TODAY analysis of gun-related slayings.

The 934 deaths account for less than 1% of all gun-related homicides, and nearly half involve a suspect slaying his or her family members, the detailed examination shows. USA TODAY combed through FBI records and news accounts to identify 146 mass shootings since 2006 that matched the FBI definition of mass shooting, where four or more people were killed.

A separate analysis of 56 mass shootings since 2009 provided to USA TODAY by a group of mayors promoting gun control reaches similar conclusions. More than half – 57% – of cases examined by Mayors Against Illegal Guns involved domestic violence. The group, co-founded by New York City Mayor Michael Bloomberg, is made up of more than 850 U.S. mayors.

"Mass shootings … are the tragedies that capture the public's attention," Mark Glaze, director of Mayors Against Illegal Guns said Thursday. "But every day, 33 Americans are being killed, mostly with handguns and distressingly often, by a family member or intimate partner."

The new data come as federal and local policymakers attempt to address gun violence in the wake of the Dec. 14 mass shooting in Newtown, Conn., that killed 20 schoolchildren and six educators at Sandy Hook Elementary School. Public revulsion over the massacre has spurred Congress to weigh a renewal of the federal assault-weapons ban and consider other gun-control measures, including a ban on magazines that exceed 10 rounds.

The mayors' group, which has joined other gun-control organizations to push for sweeping changes to federal and state firearms policies, views extending background checks on all gun buyers as a key tool in reducing gun violence. The goal is to reach private gun sales not covered by the current system, which applies only to federally licensed dealers.

The effort to close the private-sales loophole is gaining traction in Congress, where a bipartisan group of lawmakers that includes conservative Republican Sen. Tom Coburn of Oklahoma and Sen. Joe Manchin, D-W.Va., is crafting legislation.

The plan is opposed by the National Rifle Association. Its president, David Keene, said this week that the powerful lobbying group is prepared to punish lawmakers who vote to expand background checks. NRA Vice President Wayne LaPierre plans to unveil anti-background-check advertising Saturday.

Although they account for just a minuscule share of all homicides, mass killings occur about once every two weeks. More than three quarters involve a gun.

In all, 934 people have died in mass shootings over the past seven years, the USA TODAY analysis shows. In the 71 shootings that involved someone killing his or her family members, 376 victims died. Most of those killings occurred at home. Dozens more were killed by acquaintances, neighbors and co-workers.

The mayors' study also notes that just three of the 56 incidents examined by their researchers took place in schools or colleges.

The USA TODAY analysis included all the events in the mayors' study, but also dozens of others. FBI homicide records, supplied by local police, are incomplete and do not include cases from states such as Florida, which the newspaper added to its study.

Experts on mass killings say finding the right mix of policy measures to end the violence is hard.

Grant Duwe, director of research at the Minnesota Department of Corrections who has studied mass shootings, said making an effort to identify and treat people at risk of committing gun violence could be a key tool in reducing the slayings. In nearly 60% of the mass public shootings that occurred in the last century, officials found signs of mental illness, he said.

But Northeastern University criminologist James Alan Fox said offering better mental health care is no cure-all. "Mass murderers won't take you up on treatment.

"They tend to externalize and blame other people for their problems," he said. "They blame the spouse, the co-workers, immigrants. They feel persecuted.

"The kind of crime which motivates you to take action is often the kind of crime least impacted by the things we want to do," Fox added. "The only consolation is that it is a rare event."