MEMPHIS, Tenn. (AP) — A federal prosecutor told a judge Friday that he will pursue the death penalty against a former prison guard charged with killing two Tennessee postal workers.

The defendant, 48-year-old Chastain Montgomery, lowered his head but showed no other reaction to the decision by U.S. Attorney Edward Stanton when it was announced during a hearing.

Montgomery has pleaded not guilty to fatally shooting Paula Robinson and Judy Spray while robbing the Henning post office with his son in October 2010.

Prosecutors say he and Chastain Montgomery Jr., stole only $63, then shot the women in anger over the small amount.

The pair got away from the post office located about 50 miles northeast of Memphis and, according to authorities, robbed at least two Tennessee banks before the younger Montgomery was killed in a shootout with police in Mason in February 2011.

Defense attorneys have told the judge that they believe the elder Montgomery is mentally retarded. They are challenging a confession he gave authorities after his arrest at the scene of his son's death, arguing that he was not provided a lawyer during questioning and his statement was coerced by investigators.

The government's decision comes after prosecutors met with Justice Department officials in January to discuss the case.

No trial date has been set.