LOS ANGELES (AP) — Attorneys were set to deliver opening statements Monday in the trial of a doctor charged with murder in the deaths of three young men who overdosed on prescription pain killers.

Dr. Lisa Tseng has pleaded not guilty to three counts of second-degree murder. She could face up to life in prison if convicted on all the charges against her.

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Tseng, 45, is among only a handful of doctors nationwide to be charged with murder related to prescription drugs.

She operated a storefront medical clinic with her husband in Rowland Heights.

The Drug Enforcement Administration says Tseng wrote more than 27,000 prescriptions over a three-year period starting in January 2007 — an average of 25 a day.

In all, 12 of Tseng’s patients died, prosecutors say. They only filed three murder charges because they say other factors were involved in the other patient deaths.

Tseng’s attorney, Tracy Green, said in a statement that it’s “tragic whenever any patient has drug addiction or mental health issues and dies of a drug overdose.”

“However, the overdose deaths in this case were simply not Dr. Lisa’s fault,” she said. “She was just one of the links in a long sad chain. We trust the American trial process to show that Dr. Lisa is not guilty of these criminal charges.”

The three murder charges against Tseng stem from the deaths of three of her young male patients in 2009, including 21-year-old Joey Rovero, a senior at Arizona State University who grew up in the San Francisco Bay suburb of San Ramon.

Rovero’s mother, April Rovero, attended jury selection in Los Angeles County Superior Court on Friday and Monday and plans to attend the majority of the trial, which is expected to last weeks.

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“My son was a victim that needs to be represented,” April Rovero told The Associated Press. “When this happens to a child or a sibling, my experience is it changes your life irrevocably, forever. It’s not something you get over.”

She said her son never had any problems with addiction and was so aware of the dangers of alcohol that instead of driving, he once walked 2 miles home at 1 a.m. after drinking some beers with his buddies.

A toxicology report found that at the time of his death, Joey Rovero had low levels of alcohol, Xanax and OxyContin in his bloodstream, said his mother, who lives in San Ramon and founded the National Coalition Against Prescription Drug Abuse after her son’s death.

Joey Rovero died nine days after he and friends from Arizona State drove to the Los Angeles area and got prescriptions for dozens of pills from Tseng, according to court records.

During a three-week hearing in 2012 to determine whether Tseng should stand trial, the presiding judge, M.L. Villar de Longoria, found that Tseng could have reasonably foreseen the consequences of the prescriptions she wrote when her patients started dying in alarming numbers.

“She continued to prescribe these narcotics in high doses even after she was told something was terribly wrong and young men were overdosing and dying,” said Villar de Longoria.

He cited testimony about one young man who received an opiate prescription, went into the restroom at Tseng’s office and overdosed, requiring paramedics to be called.

Tseng’s attorneys at the time argued that the dead patients were to blame for making a willful choice not to follow Tseng’s instructions on how to take the drugs.

They said that Tseng treated her patients in good faith and wanted to relieve their pain.

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