New details emerged over the weekend in the mass shooting in Virginia Beach in which a gunman opened fire on a municipal building, killing 12 people. Four people remained in critical condition Sunday. The gunman, 40-year-old DeWayne Craddock, who also died from gunshot wounds, had worked at the site of the massacre for 15 years as an engineer. He emailed his resignation earlier that day, although authorities say he was in good standing at work. From 1996 to 2002, he was a member of the Virginia National Guard. Authorities say the gunman used two legally bought .45 caliber pistols and that they found two more firearms at his home. No motive has yet been found for the mass murder. On CBS’s “Face the Nation” Sunday, Democratic Virginia Senator Mark Warner called for congressional action on gun control.

Sen. Mark Warner: “This just doesn’t happen in other civilized nations at this level of violence. … I have felt that we ought to take steps against assault weapons. The suppressors, I’d like to hear what the legitimate reason is in terms of either self-defense or hunting.”

Friday’s rampage was the deadliest mass shooting in the U.S. so far this year.