JACKSON (AP) — An inmate suspected of participating in the fatal beating of a guard during a prison riot in Mississippi last year is expected to plead guilty next month.

Prosecutors say Marco Perez-Serrano, also known as Jesus Fernando Ochoa, was the first inmate to attack correction officer Catlin Carithers during the riot at the privately run Adams County Correctional Facility in Natchez on May 20, 2012.

Carithers died and 20 people were injured as the riot grew to involve hundreds of inmates.

Perez-Serrano is charged with rioting. A change of plea hearing is scheduled for Aug. 13 in U.S. District Court in Natchez.

His attorney, Joe Hollomon, did not immediately respond to a phone message.

The prison holds nearly 2,500 inmates, most of them convicted on charges of coming back to the U.S. after deportation for being in the country illegally. The prison is owned by Nashville, Tenn.-based Corrections Corporation of America, one of the nation’s largest private prison companies.

Several other inmates have been charged with participating in the riot.

Perez-Serrano was indicted in February. He pleaded not guilty in April.

An FBI affidavit filed in the case said inmates stacked food service carts from the kitchen and climbed on to a roof where Carithers was stationed with another guard.

The affidavit says Perez-Serrano was the first person seen attacking Carithers when he hit him with a food tray. After other inmates joined in the attack on Carithers, Perez-Serrano was seen hitting another guard with the tray, according to the affidavit.

The inmates used keys they took from the guards to get into secured prison areas where more correction officers were attacked, according to the affidavit. Perez-Serrano also was seen destroying prison property, including a surveillance camera, and fought with members of the special response teams that responded to the riot, authorities say.

Inmate Jesus Beltran-Rodriguez, also suspected of beating Carithers, and Humberto Cuellar, accused of taking a different guard hostage during the uprising, are scheduled for trial Oct. 7. They have pleaded not guilty to rioting.

Carithers family filed a federal lawsuit alleging that inadequate staffing and poor treatment created a dangerous environment at the facility.

In a statement after the lawsuit was filed, CCA said it “takes the safety and well-being of our staff very seriously, and we work diligently to provide our dedicated correctional officers, chaplains, nurses and teachers the training, security and support systems they need in this very challenging field.”

“In addition to conducting our own thorough review, we have cooperated fully with law enforcement throughout their investigation of the incident, and we support full prosecution of those inmates responsible for this disturbance,” the statement said.

The lawsuit, which seeks unspecified damages, said prison officials were told by an informant days before the riot that the situation was becoming volatile and that the officials failed to warn Carithers that he and other guards were on an inmate “hit list.”

Carithers was off the day of the riot but was called in to help, his family has said.

The FBI has said in court records that the riot was started by a group of Mexican inmates, known as Paisas, who were angry about what they considered poor food and medical care and disrespectful guards. Paisas are a loosely affiliated group within the prison, without ties to organized gangs, the FBI has said.

It took hours for authorities to control the riot, which caused an estimated $1.3 million in damage.

The prison’s special response team and the Mississippi Highway Patrol’s SWAT team worked to end the riot while state and area law enforcement officers, some from neighboring Louisiana, helped secure the outside.