A 29-year-old Prince William County man has admitted that he used fraudulent prescriptions to obtain thousands of tablets of oxycodone, the highly addictive pain-killer, federal prosecutors said Tuesday.

Marc Harding, of Broad Run, pleaded guilty in Alexandria federal court on Monday to conspiring to distribute the narcotic. He faces a maximum penalty of 20 years in prison at sentencing in December.

Prosecutors said that Harding created a file on his computer that became a template for a fraudulent prescription that he and other co-conspirators used to obtain more than 7,000 tablets of 30 mg Roxicodone. Hardin’s template spread to other drug rings that used it to fill illegal prescriptions for the drug, authorities said.