A Manitowoc man was arrested on Friday after he attempted to pass broken up drywall as heroin. Police responded to the report of an alleged robbery at knifepoint in the parking lot of a business in the 3400 block of Calumet Avenue around 2:20 p.m. Upon arrival, Officers learned that the victim had allegedly arranged to buy heroin but was instead sold a bag of broken up drywall for $150 by 26 year old Adam Zipperer. Once the police located Zipperer, they found several items of drug paraphernalia in his vehicle. Zipperer was arrested on suspicion of party to a crime deliver imitation controlled substance, possession of drug paraphernalia and a probation hold.