Don Spirit is pictured in this 2001 handout photo obtained by Reuters on Friday. Police identified Spirit as the man who gunned down his six grandchildren and daughter before taking his own life. Reuters/Landov hide caption

itoggle caption Reuters/Landov

Police officers take cover behind their vehicles in Moncton, New Brunswick, on Wednesday. Three police officers were shot dead and two others were injured in a shooting Wednesday night; Canadian police are searching for the suspected gunman. Ron Ward via the Canadian Press/AP/Moncton Times & Transcript hide caption

itoggle caption Ron Ward via the Canadian Press/AP/Moncton Times & Transcript

Richard Martinez, whose son Christopher Michael-Martinez was killed in Friday's mass shooting in Isla Vista, Calif., breaks down as he talks to media outside the Santa Barbara County Sheriff's headquarters on Saturday. Jae C. Hong/AP hide caption

itoggle caption Jae C. Hong/AP

Newtown, Conn., Dec. 20, 2012: Stuffed animals and a candle arrangement at a streetside memorial for the 20 children and six adults killed at Sandy Hook Elementary School. John Moore/Getty Images hide caption

itoggle caption John Moore/Getty Images

Former Arizona Rep. Gabrielle Giffords, accompanied by her husband, retired astronaut Mark Kelly, speaks during a news conference in Manchester, N.H., in July. They were there to encourage state political leaders to have courage in the fight to expand background checks on gun purchases. Mary Schwalm/AP hide caption

itoggle caption Mary Schwalm/AP

President Obama speaks during a memorial service at the Marine Barracks Sunday in Washington, D.C., honoring victims of Monday's shooting at the Navy Yard. Brendan Smialowski/AFP/Getty Images hide caption

itoggle caption Brendan Smialowski/AFP/Getty Images

Police say Aaron Alexis, who was killed Monday, gunned down 12 people at the Washington Navy Yard. FBI/Reuters/Landov hide caption

itoggle caption FBI/Reuters/Landov