A former Gwinnett County sheriff’s deputy has been indicted on federal charges after authorities said he used excessive force against a female inmate and lied about it in an incident report.

U.S. Attorney BJay Pak said Aaron S. Masters, 27, of Jefferson, repeatedly punched the inmate in the head in 2018 and then tried to justify the assault when he reported it.

“We recognize that corrections officers have a difficult job as they maintain order and protect inmates in our district's prisons and county jails,” Pak said. “However, this deputy sheriff must be held accountable for allegedly abusing his authority by committing a violent and unnecessary assault on an inmate, and then writing a false report to cover up the incident.”

Masters was on the Rapid Response Team in the Gwinnett jail at the time of the incident, according to Pak. The RRT is a special unit that responds to high-risk incidents in the jail.

Officials said Gwinnett inmate Shelby Clark, who was jailed on a simple battery charge, attacked several deputies Aug. 20, 2018, AJC.com previously reported.

MORE: Grand jury asks for more records about use of force at Gwinnett jail

The deputies subdued Clark and were treated for their injuries, Deputy Shannon Volkodav previously told AJC.com.

However, when she was returned to her cell, Clark began harming herself, Volkodav said. Deputies, including Masters, went into her cell to keep her from hurting herself, she said.

It was during that exchange that Masters struck Clark in the face with a closed fist, Pak said. Clark suffered a black eye and a bruised cheek.

“Following the assault, Masters wrote a report about the encounter in which he falsely claimed that the physical force was necessary to gain the inmate’s compliance,” Pak said.

Masters was arrested and locally charged with battery in August 2018. He resigned from the sheriff’s office shortly after turning himself in.

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Federal prosecutors charged Masters with violating an inmate’s civil rights and writing a false report.

RELATED: Gwinnett sheriff's 'rapid response team' under federal investigation

The incident occurred exactly a week before court filings revealed that a federal grand jury was conducting a criminal investigation into the agency’s “rapid response team.”

The filing was made as part of an ongoing federal lawsuit filed in 2013 over the RRT’s use of “restraint chairs,” devices designed to hold unruly inmates’ arms, legs, chest and head in place. The civil lawsuit — filed in U.S. District Court in Atlanta, initially on behalf of a dozen or so former Gwinnett inmates — alleges that the chairs amount to excessive force and were inappropriately used as punishment.

The woman was seen on video being punched repeatedly by a deputy.