NATCHEZ (AP) — A federal judge has delayed the trial of a man charged with participating in a deadly prison riot in Mississippi because the defendant is undergoing a psychiatric examination.

One guard was killed and 20 people were injured in the May 20, 2012, riot at the privately-run Adams County Correctional Facility in Natchez, which holds immigrants convicted of crimes while being in the U.S. illegally.

Humberto Cuellar is accused of taking a guard hostage during the uprising.

His trial had been scheduled to begin Monday, but his lawyer asked for the delay due to the examination.

The trial is now set for the court term beginning Dec. 2 in U.S. District Court in Natchez.