A deadly riot at a prison for illegal immigrants in Mississippi was started by a group of Mexican inmates angry about what they considered poor food and medical care and disrespectful guards, according to an FBI agent's affidavit.

One guard was killed and 20 people were injured in the May 20 riot at the privately-run Adams County Correctional Facility in Natchez, which holds illegal immigrants convicted of crimes in the United States.

The leaders of the Mexican inmates, known as the Paisas, demanded to take a list of grievances to the warden that day and told others in the group to disobey orders from prison staff, according to the FBI affidavit. The affidavit, filed last week in U.S. District Court in Jackson, is part of a complaint charging one of the inmates with rioting.

Correction officer Catlin Carithers was beaten to death during the riot, which officials have said involved as many as 300 inmates and left the prison badly damaged. The affidavit does not say who killed Carithers.