A state prison inmate is charged with murder in the death of another inmate in June. 49-year-old Frank Higgins is accused of killing Lloyd Millett. State police say Millett was assaulted at the prison on May 24th. He died two weeks later. Higgins was charged Friday with murder, one day after he was indicted by the Knox County Grand jury. Both he and Millett were already serving prison sentences for murder. Higgins was convicted of killing a woman in her home in Kenduskeag in 1999 and was sentenced to 45 years in prison. Millett was convicted of killing two women in 1995 in Lewiston and Turner.Higgins is expected to make his first court appearance on the new charge next week.