SAN FRANCISCO (CBS SF/AP) — A Santa Rosa doctor has become the first California doctor charged with second degree murder for over-prescribing opioids to his patients, according to state Attorney General Xavier Becerra.

Becerra filed multiple criminal charges against 72-year-old Dr. Thomas McNeese Keller related to nine of his patients. The charges include second-degree murder in four deaths and felony elderly abuse for a fifth patient who also died. The murder charges could bring a life sentence.

Thomas Keller (Sonoma County Sheriff’s Office)

It’s the first time that a California attorney general has filed murder charges against a doctor for overprescribing opioids, Becerra’s office said.

Last year, state prosecutors persuaded a state appeals court to uphold the second-degree murder conviction of a former osteopathic doctor, Hsiu Ying Tseng, who is serving a life sentence for the overdose deaths of three patients, but those charges were initially filed by a local prosecutor.

Keller’s defense attorney, John Cox of Oakland, said his client is a longtime pain management doctor, and several of his patients killed themselves and another died of an accidental drug overdose.

He “has always, to the best of his medical ability, attempted to take good care of his patients,” Cox said. “There are no grounds for murder charges in this case.”

Becerra filed his charges after the federal government sought to prosecute Keller last year on the more limited charges of overprescribing medications.

Keller was arrested Monday and remains jailed in Sonoma County awaiting a bail hearing next week.

The charges allege that between 2011 and 2017 Keller drastically increased his patients’ opioid prescriptions while also prescribing other drugs that can cause a dangerous interaction.

They say he prescribed Vicodin, oxycodone, OxyContin, Percocet, and morphine at levels well beyond accepted medical practice.

He would often prescribe 180 to 300 pills in each prescription despite urgent warnings from pharmacies and insurance companies and even after some patients died of drug overdoses, Becerra said.

“Doctors take an oath to protect patients and not engage in behavior that can risk their health and safety,” Becerra said in a statement. “When we see evidence of a crime and patient harm, we must act. The opioid epidemic is destroying our communities and taking our loved ones.”

Cox called the murder charges “an effort to grab attention related to the opioid crisis,” saying he looks forward to exonerating his client.

The charges came from an investigation of his Bureau of Medi-Cal Fraud and Elder Abuse that investigates abuse, neglect, and fraud against elderly and dependent adults in care facilities.