Kelly's lawyers filed a motion Friday in federal court to question Jeremiah Farmer under oath, the Chicago Tribune reported.
Farmer said in a court filing earlier this week in Hammond, Indiana, that he attacked Kelly on Aug. 26 in the Metropolitan Correctional Center because he wanted to shed light on wrongdoing by the government in his own criminal case. He said he was frustrated about his limited access to a computer because of COVID-19 restrictions, according to the document.
Farmer was able to slip away from an employee at the center, enter a cell and repeatedly hit Kelly in the head, according to a U.S. Bureau of Prisons report attached to Farmer's filing.
A security officer used pepper spray to stop the attack. A lawyer for the singer says he suffered cuts and bruises from the attack.
Kelly, 53, faces several dozen counts of state and federal sexual misconduct charges in Illinois, Minnesota and New York, from sexual assault to heading a racketeering scheme aimed at supplying him with girls. The Grammy Award-winning singer has denied ever abusing anyone.
Farmer, 39, is facing mandatory life in prison in a racketeering conspiracy that involved a 1999 double murder, according to the newspaper.
"It appears that MCC personnel simply followed Mr. Farmer, allowed him to carry out the attack, and then only intervened after Mr. Kelly had already sustained serious injuries," Kelly's attorney Michael Leonard wrote in the motion.
Kelly's attorneys have been trying to have him released on bond pending his trial.
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ABC7 Chicago contributed to this report.