A former Alexandria doctor pleaded guilty Tuesday to conspiring to distribute hundreds of thousands of painkilling pills to people who had no medical need for the drugs.

Larren Wade, 55, faces a maximum penalty of 20 years in prison when he is sentenced on May 17.

"Larren Wade not only violated his oath as a doctor, he violated the law," said U.S. Attorney Neil MacBride.

The FBI investigation began in early 2010, when Virginia and local police discovered a street-level pill-dealing network operating in the Lorton area, and several pill dealers had been supplied through prescriptions by Wade.

Police also had received a number of complaints that his patients were injecting drugs in the parking lot in front of his practice on the 5100 block of Dawes Avenue.

Undercover officers found long lines at the doctor's office. They were able to bribe an office worker and jump ahead in line.

During one of the visits, undercover officers asked Wade if they could get prescriptions for a "friend." The friend did not exist.

The undercover officer paid Wade an $85 office visit fee for the fictitious patient, and the doctor wrote out two more prescriptions and created a patient file for the "friend," according to charging documents.

Prosecutors said Wade operated an almost strictly-cash business and would see between 30 and 50 patients per day. He once saw more than 100 patients in a single day and collected nearly $10,000 in cash, prosecutors said.

During a seven-month period in 2010, Wade filled out about 7,000 prescriptions for oxycodone, hydromorphone and methadone, for a total of 900,000 tablets, prosecutors said.

Wade frequently issued prescriptions without conducting a physical exam, without reviewing medical records and without establishing a treatment plan.

In May 2010, an investigator with the Virginia Board of Medicine met with Wade to address concerns raised by several pharmacies about the prescriptions he was writing.

Wade provided the investigator a three-page, handwritten document that had been given to Wade by one of his patients. The document listed the names of 20 of Wade's patients who were alleged to have been selling the medications that he supplied.

The document also listed "users" and "paid confidential informants."

According a prosecutors, Wade continued to provide subscriptions for more than 10,000 pills to the patients he suspected of being drug dealers.