The prosecutor on Wednesday painted all three defendants as conspirators who fed the celebrity's desire for prescription drugs. Prosecutors call Stern an aider and abettor of the two doctors who are charged with improperly prescribing the drugs that killed Smith.
Stern's attorney, Steve Sadow, was the first to present the defense position.
He said jurors would not be able to find a bad motive for Stern's actions. But he separated him from the other defendants.
Sadow said Smith had dealt with "chronic pain" dating back to 2000, and that Stern -- who was "with her constantly" -- had heard her complaints of pain.
Smith's mother, Virgie Arthur, looked on from the back row of the downtown Los Angeles courtroom, as the trio's trial got under way.
The former Playboy Playmate died on Feb. 8, 2007 from an accidental prescription drug overdose in a Florida hotel room.
She had been living in the Bahamas and was allegedly receiving deliveries of prescription medications from her Los Angeles-based doctors.
Eroshevich's attorney, Bradley Brunon, said the two women were friends and neighbors and when Smith's son died of a drug overdose, she called her friend for help. He said Eroshevich rushed to bring drugs to her in the Bahamas. He said the controversial order for drugs were never meant to be given all at once. He said they were part of a plan to try each drug and see which one would work best.
The autopsy showed that the 39-year-old had nine different medications in her system.
Deputy District Attorney Renee Rose displayed pictures on a courtroom screen of prescriptions for hundreds of pills, including Dilaudid, a drug known as "hospital heroin," and methadone in pill, liquid and injectible form.
"Anna Nicole Smith took a lot of methadone for pain and she took Dilaudid on top of that," Rose said.
The defendants' lawyers have suggested they were desperately trying to save the doomed model during a period when she gave birth to a daughter and lost her son.
Authorities claim that 44 different medications were prescribed for Smith under a number of other names, including Stern's. According to Sadow, the fake names used were to keep Smith's medical issues out of the eye of prying media.
Stern says he was just following the doctors' orders. Not a single hospital used her real name, including Cedars Sinai.
Kapoor's lawyer, Ellyn Garafalo, said Wednesday that Kapoor's prescriptions were appropriate and worked, and "he managed her pain and he acted in good faith."
If convicted all three defendants could face more than five years in prison and the doctors would lose their medical licenses.
Superior Court Judge Robert Perry said Smith's cause of death is not an issue, although some jury members said they already know she died of a drug overdose. They promised to disregard that information.
"What we are trying is a legality of prescribing medication case," he said.
After hearing 17 witnesses in the preliminary hearing, Perry concluded that the trio of defendants cared deeply for Smith but said there was sufficient evidence to support convictions if a jury should find them guilty.
The jury is made up of six women and six men. The panel includes a registered nurse and a hospital employee who works with drug addicted mothers. Along with the 12 jurors, five women and one man were chosen as alternates.
The Associated Press contributed to this report.