The nation’s largest gun-rights lobby on Friday called for armed officers to be placed in every American school, saying, “The only thing that stops a bad guy with a gun, is a good guy with a gun.”

Breaking its silence a week after the shooting in Newtown, Conn., that left 20 children dead, the National Rifle Association blamed the media, a culture of violence and the lack of armed school security guards, among other factors, for such mass killings.