Mattox, who is free on bond and wearing a GPS monitor, is scheduled to appear in court June 3, according to court documents.
Court records filed in Butler County Area II court said Lay confessed to killing Risner, a mother of three sons.
Police were called shortly before 4 p.m. Feb. 4 on a report of an unresponsive person. Risner was pronounced dead at the scene, and her death was ruled a homicide by the Butler County Coroner’s Office.
The house and Risner had been the subjects of a drug investigation by the Warren County Drug Task Force for months before the homicide, according to court documents.