(CNN) -- The two Ohio prison guards responsible for checking on imprisoned Cleveland kidnapper Ariel Castro "did not timely perform" required rounds, the Ohio Department of Rehabilitation and Correction said Thursday.
The agency said they appeared to have falsified "the post log book for their rounds,"
Castro, who was held at the Correctional Reception Center in Orient, was found hanged with a bed sheet last month. Prison medical staff tried to revive him.
The guards were placed on leave as investigators looked into Castro's suicide. Any disciplinary action, which could include termination of employment, will be determined by the Ohio State Highway Patrol at the conclusion of its investigation.
Castro pleaded guilty in August to 937 counts, including the kidnapping of Michelle Knight, Georgina DeJesus and Amanda Berry. He was sentenced to life plus 1,000 years.