A Maryland state prison inmate has been charged with first-degree murder in the strangulation of his cellmate last December.

The Allegany County State's Attorney's Office says a grand jury indicted 25-year-old Brian Cotter Wednesday in the killing of 57-year-old Lewis Thompson Jr.

Thompson was found unresponsive in a cell at North Branch Correctional Institution Dec. 11. He had been serving a 40-year sentence on an Anne Arundel County rape conviction.

Cotter, of Dundalk, is serving a life sentence for the 2007 murder of Raymond Zubrowski.

Court records do not list a defense attorney for Cotter in the latest case.