A Kansas doctor has been charged with operating a pill mill for pain killers and antidepressants after Fort Riley officials raised concerns about soldiers who overdosed.

The U.S. attorney’s office alleged in a criminal complaint Tuesday that 53-year-old Michael P. Schuster conspired to illegally distribute controlled substances.

The affidavit says the investigation began last year when police received reports that Schuster was issuing high-dosage prescriptions based on limited physical examinations, leading to several overdoses. Medical staff at Fort Riley also reported that Schuster had treated active duty soldiers and family members who died from overdoses. More than 500 prescriptions were written while Schuster was out of the office.

A phone message left for Schuster’s attorney, Barry Clark of Manhattan, wasn’t immediately returned.