An eastern Iowa man says he’s innocent in last year’s murder at the drug treatment clinic where he was living. The man accused of killing 44-year-old Kathi Mertens of Mount Pleasant pleaded not guilty to first-degree murder on Tuesday. The trial for 19-year-old Ryan Wichart of North Liberty is set for April 4th. Police say Wichart strangled Mertens on November 16th in an attempt to get prescription drugs. Mertens’ body was found that morning, locked in a medication storage room at the Burlington Alcohol and Drug Dependency Services Center where she was a counselor-aide.