California neurosurgeon Dr. Thomas McNeese Keller, 72, has been charged with murder following the deaths of five of his patients due to opioid overdose.

Earlier this week, on Monday, August 12, the office of the California State Attorney General arrested Dr. Thomas McNeese Keller on four charges of second-degree murder. If convicted, he faces a sentence of 60 years to life in prison. 

Dr. Keller, 72, allegedly prescribed his patients upwards of 180 opioid painkillers such as Vicodin, Oxycontin, Percocet, and Morphine at a time, 'levels well outside accepted medical practice,' said Attorney General Xavier Becerra. 

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Five of the patients in his care died of opioid overdoses - one in 2015, two in 2016, and two in 2017. 

Santa Rosa doctor, Thomas Keller, 72, is facing 2nd degree murder charges after state authorities say he's responsible for killing five patients by giving them an obscene amount of pain pills. https://t.co/hEpYOouKBy

— KRON4 News (@kron4news) August 16, 2019

Opioid addiction has been labeled as an epidemic in the United States, where close to 50,000 people die annually due to opioid overdoses. 

Dr. Keller's case marks the first time that the California attorney general's office has charged a doctor who prescribed opioids with murder.

The first case in which a doctor was charged and convicted with murder for overprescribing opioid drugs to patients who then overdosed also took place in California, in 2015: Dr. Hsiu-Ying “Lisa” Tseng was found guilty of second-degree murder in the deaths of three patients and received a sentence of 30 years to life. 

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"Doctors take an oath to protect patients and not engage in behavior that can risk their health and safety. When we see evidence of a crime and patient harm, we must act," Attorney General Becerra said. 

"The opioid epidemic is destroying our communities and taking our loved ones. The California Department of Justice will continue to prosecute fairly and diligently all those who are alleged to have abused our health care system and over-prescribe drugs at the expense of their patients," he added. 

California attorney general Xavier Becerra sees state playing major role in opioid legal fight https://t.co/eglsaXWPaZ

— Bloomberg (@business) August 22, 2018

Keller's attorney, John Cox, accused the state's attorney general's office of "absolutely overreaching in an effort to try and show they are doing something about the opioid crisis. Dr. Keller has been a pillar in the Santa Rosa community as a health care professional for many, many years."

Dr. Keller received his degree from UC Davis School of Medicine and served as a neurosurgeon in the US Army and Air Force. Keller opened a private medical practice in Santa Rosa in 2011, the Daily Mail reports.

His medical license was previously revoked in 1990 after he was convicted on three charges of battery. According to the San Francisco Chronicle, he was also accused of sexual abuse by eight patients. His license was reinstated in 1994 after Dr. Keller completed mandated therapy and supervised medical volunteer work.

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Criminal charges against Dr. Keller were filed in Sonoma County's California Superior Court on August 8.  They consist of four charges of second-degree murder, one charge of elder abuse, and "prescribing drugs without a legitimate medical purpose," the Chronicle reported

Prior to these charges, Dr. Keller was already under investigation by the California state medical board due to accusations that he had needlessly prescribed patients excessively high doses of narcotics and failed to appropriately screen patients for overdose risk prior to writing prescriptions. 

Prescription opioid drugs in front of the American flagGetty Images