LOS ANGELES » A doctor was convicted of second-degree murder Friday for the overdose deaths of three patients, capping a case that was closely watched by medical professionals across the country.

Hsiu-Ying “Lisa” Tseng of Rowland Heights, a community in Los Angeles County, was the first doctor charged with murder in California for prescribing drugs to patients who fatally overdosed. She was accused of ignoring “red flags” about her prescribing habits, including the overdose of a patient in her clinic and nine phone calls in less than three years from authorities informing her that patients had died with drugs in their system.

During the trial, which lasted nearly two months, Deputy Los Angeles County District Attorney John Niedermann told jurors that even after some patients — among them an undercover agent — told Tseng about their heroin addiction, she agreed to give them powerful narcotics without asking follow-up questions.

“She wrote them a prescription for the very thing they’re addicted to,” Niedermann said. “She shoved them over that cliff.”

Tseng’s defense lawyer portrayed the doctor as overworked and too trusting of her patients, saying she did not realize how common it was for people to abuse prescription drugs.

“She got in over her head,” attorney Tracy Green told the jury.

Although the state’s medical board had found Tseng, 45, in violation of some standards, Green said that didn’t mean her client’s actions were criminal.

“That’s what malpractice cases are about,” Green said. “She did not murder people.”

Tseng is one of only a few doctors across the country charged with murder for prescribing painkillers that led to a patients’ death. Last month, a Florida physician was acquitted of first-degree murder in a patient’s overdose death.

Other doctors have faced lesser charges. In 2011, a L.A. County jury convicted Conrad Murray of involuntary manslaughter for giving Michael Jackson a surgical anesthetic that killed him.

Tseng’s trial drew close attention from the medical world. Some experts worried that a conviction would trigger a dangerous chilling effect for worried doctors and keep powerful painkillers from patients who need them.

Prosecutors charged Tseng with second-degree murder for the deaths of Vu Nguyen, 28, of Lake Forest; Steven Ogle, 25, of Palm Desert; and Joey Rovero, 21, an Arizona State University student who prosecutors say traveled more than 300 miles with friends from Tempe, Ariz., to get prescriptions from Tseng at her Rowland Heights clinic.

Prosecutors also accused her of several felony counts of prescribing drugs to people with no legitimate need for the medications. and a count of fraudulent prescribing for writing a man’s name on prescriptions so his wife could double her pill count.

A 2010 Los AngelesTimes investigation found that at least eight of Tseng’s patients died of overdoses from the same type of drugs she prescribed to them.

During closing arguments, the prosecutor asked jurors to think about the testimony of Dr. Gene Tu — Tseng’s husband, who has also faced medical board discipline. Tu testified that phone calls from coroner’s officials informing Tseng that her patients had overdosed “didn’t create an issue in the office.”

The prosecutor argued that Tseng didn’t care about her patients’ treatment and sometimes referred to them as “druggies.” For her, he said, it was about “dollars and cents.”

From 2007 — the year Tseng joined the Rowland Heights clinic where her husband worked — to 2010, Niedermann said tax returns show that their office made $5 million.

“Why would somebody do this?” the prosecutor asked, glancing at Tseng. “Five million reasons.”

Tseng’s attorney argued that her client’s actions weren’t motivated by the money.

Although Tseng “could’ve practiced medicine better,” Green said, the doctor cared about her patients and often explained to them that they didn’t need the types of drugs they wanted.

“She’s not just giving them out,” Green said. “She’s warning them how dangerous they are.”