A Maine State Prison inmate has been indicted on aggravated assault and murder charges. Guy Hunnewell, 42, is accused of killing a fellow inmate in June. Police say Hunnewell attacked Alan Powell, 57, in an exercise area of the prison. The medical examiner ruled the death a homicide and said Powell died from blunt force trauma to the head.The aggravated assault charge is from a separate reported incident.Powell was serving a life sentence for murdering a woman in Waterville. Hunnewell is serving a 40 year sentence for killing his girlfriend. Hunnewell is scheduled to be in court on August 28th for an arraignment.