Updated

A federal judge has ruled that a former prison guard charged with killing two rural Tennessee postal workers is eligible to face the death penalty at trial.

U.S. Senior District Judge Jon P. McCalla ruled Tuesday that Chastain Montgomery is not mentally disabled and thus eligible to face the death penalty on charges that he killed Paula Robinson and Judy Spray in the post office in rural Henning in October 2010.

Prosecutors say the women were fatally shot during a robbery committed by the 50-year-old Montgomery and his 18-year-old son Chastain Montgomery Jr.

Defense attorneys argued that Chastain Montgomery is mentally disabled and ineligible for the federal death penalty under U.S. law. Psychologists have testified that three IQ tests show Montgomery has a mild intellectual disability, with scores under 70.