South Dakota death row inmate Eric Robert to be executed by lethal injection Monday night

South Dakota is set to execute its first prisoner on death row in five years and only the second in more than six decades.

Fifty-year-old Eric Robert is to die by lethal injection at 10 p.m. Monday. Groups opposed to the death penalty plan a vigil outside the State Penitentiary in Sioux Falls.

Robert pleaded guilty in the April 2011 slaying of prison guard Ronald Johnson during a failed escape attempt. Robert asked to be put to death, saying he would kill again.

Another prisoner who pleaded guilty in the killing was sentenced to death but has appealed the sentence. A third inmate received a life sentence for providing materials used in the slaying.