In 2010, Omar Thornton killed eight colleagues in Manchester, Conn., before killing himself. Private employers used to create their own rules about guns on their property. But over the past five years, many states have adopted laws that allow employees to keep firearms in their vehicles at work. Douglas Healey/Getty Images hide caption

itoggle caption Douglas Healey/Getty Images

Community members and students from Marysville-Pilchuck High School gather for a vigil at the Grove Church in Marysville, Wash., Friday night. Two students died in the violence, including the gunman. Several more were wounded. David Ryder/Getty Images hide caption

itoggle caption David Ryder/Getty Images

Surrendered handguns are piled in a bin during a gun buyback event in Los Angeles on May 31, 2014. David McNew/Getty Images hide caption

itoggle caption David McNew/Getty Images

Fifth-graders from the Bradwell School of Excellence in Chicago's South Shore area wrote an op-ed piece for The Chicago Tribune this week, explaining how they see their neighborhood. Google hide caption

itoggle caption Google

Police cordon off the area around a shooting in Chicago Wednesday. The violence broke out down the street from where NPR's David Schaper was conducting an interview about urban renewal efforts. David Schaper /NPR hide caption

itoggle caption David Schaper /NPR

A makeshift memorial sits in front of IV Deli Mart, where part of Friday night's mass shooting took place in the Isla Vista, Calif., community. The parents of Elliot Rodger, accused of killing six people, were reportedly rushing to try to stop their son when they heard about the violence. Chris Carlson/AP hide caption

itoggle caption Chris Carlson/AP

Michael Dunn reacts after the verdict is read in Jacksonville, Fla., on Saturday. Dunn was convicted of attempted murder in the shooting death of a teenager over an argument over loud music, but jurors could not agree on the most serious charge of first-degree murder. Bob Mack/The Florida Times-Union/AP Pool hide caption

itoggle caption Bob Mack/The Florida Times-Union/AP Pool

A police officer walks out of the Electrical Engineering Building on the campus of Purdue University in West Lafayette, Ind., Tuesday. One person was killed in a classroom by a gunman who surrendered to a police officer within minutes of the attack, officials said. Michael Conroy/AP hide caption

itoggle caption Michael Conroy/AP

An image from a Connecticut State Police report on the shootings at Sandy Hook Elementary School shows a scene at 36 Yogananda St. in Newtown, Conn., where Adam Lanza killed his mother before driving to the school and killing 26 students and staff last December. AP hide caption

itoggle caption AP

Theodore P. Wafer, 54, charged with second-degree murder in the shooting death of Renisha McBride, appears at his arraignment in Dearborn Heights, Mich., on Friday. Paul Sancya/AP hide caption

itoggle caption Paul Sancya/AP

Officers on Capitol Hill look at a car following Thursday's shooting, which left Miriam Carey, 34, dead. "We're still very confused as a family why she's not still alive," Carey's sister says. Charles Dharapak/AP hide caption

itoggle caption Charles Dharapak/AP