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.

RELATED: Ex-Gwinnett deputy arrested after allegedly hitting inmate

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.