Editor's note: This article has been updated throughout.

Sherman physician Howard Gregg Diamond pleaded guilty to drug distribution and fraud charges in federal court Friday, amid allegations he unnecessarily prescribed powerful painkillers over a span of at least seven years, leading to the overdose death of one person in 2015.

In an emailed press release distributed Friday by the office of U.S. Attorney Joe Brown, the agency said Diamond, 57, pleaded guilty to conspiracy to possess with intent to distribute controlled substances and aiding and abetting health care fraud before U.S. Magistrate Judge Christine Nowak. Under the plea agreement, Diamond waived his right to an appeal, forfeited his physician’s DEA registration number and faces a possible sentence of up to 20 years in prison.

“Physicians like Dr. Diamond have been fueling the opioid crisis in this country,” U.S. Attorney Joe Brown said in the release. “The number of pills that he was putting out on the street was shocking. And in this case, death was linked to those pills. Undoubtedly, others’ addictions were worsened, and families suffered as a result. To reduce the impact of opioids, doctors have to take their obligations seriously, and if they don’t, there will be more prosecutions like this.”

Diamond’s defense attorney Pete Schulte said his client never intended for his prescriptions to be abused by his patients or cause any harm.

“I believe Dr. Diamond was trying to be a good doctor and help these people,” Schulte said. “Mistakes were made, a patient died and he accepts full responsibility for that.

According to the release, prosecutors alleged that, beginning in 2010, Diamond issued prescriptions for hydrocodone, oxymorphine, methadone, fentanyl, morphine, oxycodone, alprazolam and zolpidem through his Sherman and Paris medical offices and did so without a legitimate medical purpose. Prosecutors said Diamond prescribed multiple medications, including morphine and oxycodone, to an individual on July 15, 2014, who then died as a result of taking the drugs, just 10 days later. Diamond also submitted a reimbursement claim to Medicare, in which he told the agency he treated a patient of the program in Sept. 2015, but prosecutors contended Diamond wasn’t even in the state at the time.

“That was a result of his office billing Medicare for times that his PA saw them, but they billed it at the time that Gregg saw them,” Schulte said of the fraud charge. “So they ended up getting more money.”

The Centers for Medicare and Medicaid Services reported that, in 2014, Diamond’s opiod count was listed at 11,035 — a figure which made him the 24th-highest prescriber of such medications in the nation that year. In August 2015, the Texas Medical Board took disciplinary action against Diamond after the organization found he failed to maintain adequate medical records. Diamond successfully completed the requirements of the disciplinary order, but his troubles with law enforcement continued.

In April 2017, Diamond took to social media and acknowledged that multiple pharmacies in the area had begun to refuse his prescriptions and, one month later, DEA investigators executed search warrants at his Sherman office. Diamond was arrested by the FBI in July 2017 and in a prepared statement, the Texas Medical Board said it temporarily suspended his license “after determining his continuation in the practice of medicine poses a continuing threat to public welfare.” A grand jury indicted Diamond on 21 charges that same month, connecting him to the deaths of seven patients who died within days or weeks of receiving their prescriptions, including three people living in the Texoma area. Diamond’s medical license was officially revoked by the medical board in October 2017.

Schulte said he and his client had sympathy for the other six patients and their families — many of whom attended Friday’s hearing — but evidence his defense team amassed suggested those patients may have been taking other prescriptions and illegal drugs, without Diamond’s knowledge.

“Through our investigation, we were able to show the U.S. Attorney’s office why the plea agreement we reached was justice for everybody involved,” Schulte said.

According to the U.S. Attorney’s Office, the case has been prosecuted under the Organized Crime Drug Enforcement Task Force and has been investigated by a host of agencies, including the DEA, the Department of Health and Human Services, Internal Revenue Service, the FBI, the Sherman Police Department, the Ellis County Sheriff’s Office and the Texas Office of the Attorney General. It is being prosecuted by Assistant U.S. Attorney Heather Rattan and Maureen Smith.

A sentencing hearing for Diamond will be scheduled after the completion of a presentence investigation by the U.S. Probation Office. Schulte said Diamond will serve out at least 85 percent of his sentence with good behavior as federal law dictates, and would receive credit for the 18 months he has served in the Fannin County Jail.

“He’ll spend the next 15 years in prison,” Schulte said.