SIOUX FALLS, S.D. — A South Dakota inmate was executed Monday for killing a prison guard in a failed escape seven years ago in the state's first execution since 2012.Rodney Berget, 56, was put to death for the 2011 slaying of Ronald "R.J." Johnson, who was beaten with a pipe and had his head covered in plastic wrap at the South Dakota State Penitentiary in Sioux Falls.