DALLAS (CBSDFW.COM) – A Dallas doctor who oversaw the illegal prescription of nearly one million units of narcotics with no legitimate medical purpose was sentenced to 13 years in federal prison Monday.

Carlos Luis Venegas, 62, was convicted of conspiracy to distribute a controlled substance following a five-day trial in early February.

READ MORE: Basketball Hall Of Famer's Shop With A Cop Program Helps Build Trust Between Police And Kids

According to evidence presented at trial, Dr. Venegas acted as the supervising physician for a series of sham medical clinics – all fronts for the illegal distribution of Hydrocodone and Alprazolam.

“These pill mills help to perpetuate the tragic opioid crisis gripping our country,” U.S. Attorney for the Northern District Erin Nealy Cox said following the guilty verdict. “Last year, America lost, on average, 116 people per day to opioid overdoses. We cannot allow unscrupulous conduct by physicians to add to the supply of dangerous drugs on the streets.”

“The DEA will continue to investigate these types clinics and health care personnel who are facilitating illegal distribution of prescription drugs”, said DEA Special Agent in Charge of the Dallas Field Division Clyde E. Shelley, Jr. “One overdose is one too many.”

At trial, witnesses testified that members of the conspiracy paid homeless and indigent people to pose as patients seeking pain medication.

READ MORE: Hundreds Come Out To Honor Fallen Mesquite Officer In Prayer Vigil

Runners coached the men and women on how to describe their (nonexistent) symptoms, drove them to the clinics, and paid for their appointments.

At the clinics, nurse practitioners and physician’s assistants, working under Dr. Venegas’ supervision, conducted only cursory medical exams, witnesses said. Medical files seized from the clinics showed that most exams were conducted without any medical testing and rarely produced documentation of patients’ purported ailments.

At the end of the visits, patients were almost always prescribed a cocktail of medications, including Hydrocodone and Xanax, generally for the highest dosages available.

Several of Venegas’ codefendants, including several nurse practitioners and clinic managers, previously pleaded guilty to their roles in the scheme.

Codefendant sentences include:

MORE NEWS: Oklahoma Hires Clemson's Venables As Coach

· Christan Michael Hicks – 70 months
· Craig Zahn – 33 months
· Leslie Rodriguez – 33 months
· Don Broussard – 33 months
· Ron Cunningham – 18 months
· James Christopher Ware (co-owner of clinics, charged in a separate indictment) – 135 months
· Stanley James (co-owner of clinics, also charged in a separate indictment) – 97 months