Federal prosecutors say the former prison guard charged with killing two Henning postal workers was planning an escape from custody.
In court documents filed Friday, prosecutors say Chastain Montgomery was collecting plastic trays and he was planning to turn them into shanks.
Prosecutors say he was also going to attack a U.S. Marshal while being transported to a court appearance. Montgomery attacked a corrections officer instead, when the trays were discovered.
Montgomery has pleaded not guilty to killing Paula Robinson and Judy Spray while robbing the Henning post office with his 18-year-old son in October 2010.
The government is seeking the death penalty at trial. No date has been set.