California authorities investigating reality TV star Anna Nicole Smith's untimely death served two of her doctors search warrants Friday and raided six different locations, including the physicians' offices and residences.

State Attorney General Jerry Brown said Friday that detectives had "serious evidence" in the case, but declined to elaborate further and wouldn't provide the names of the doctors, saying only they were among those who had prescribed medication to Smith. No arrests have been made, he said.

But a law enforcement source told FOX News that the two doctors who have come under scrutiny in Smith's death, Dr. Sandeep Kapoor and psychiatrist Dr. Khristine Eroshevich, were the targets of Friday's warrants.

Kapoor and Eroshevich were served with a total of eight warrants, according to the source. Smith's attorney and companion, Howard K. Stern, was at the home of Eroshevich when agents showed up with the warrants Friday, sources said.

"We've learned quite a lot, but we don't want to jeopardize the investigation by prematurely releasing what we've found," said Brown in a news conference. "I'm not going to speculate on charges. But someone is dead."

Ellyn Garafalo, a lawyer for Kapoor, who prescribed methadone to Smith shortly before she died, confirmed the doctor's home and offices were among those raided but declined to comment further.

Agents from the California Department of Justice answered a knock on the door of one of Eroshevich's offices Friday morning, but declined to say why they were there.

They said the doctor was not in and provided a phone number for the department's office of public information, which had no immediate comment.

A call to Eroshevich's attorney, Gary Lincenberg, was not immediately returned.

Brown told reporters that other physicians and pharmacists were also being interviewed as part of the investigation.

Smith, a former Playboy Playmate, died of an accidental overdose of drugs, including a powerful sleep aid, in February at a Florida hotel. She was 39.

To date, detectives have collected more than 100,000 computer images, files, patient profiles and other documents as part of the probe into the cause of Smith's sudden death, Brown said.

"We're looking into a number of possible violations," he said. "You don’t go to a judge and get a search warrant for somebody’s home unless you think a rather serious crime has been committed."

The California Medical Board and other agencies were assisting in the probe, according to the attorney general.

County prosecutors were aware of the raids but were not involved in the operation, said spokeswoman Sandi Gibbons. She confirmed the searches were conducted but declined to name the physicians.

The raids being conducted throughout the Los Angeles area are the first public signs that friends and associates of the starlet are under criminal investigation in California.

Several people close to the model have fallen under suspicion since her death.

The Medical Board of California said in April it was investigating Eroshevich, who, according to documents, authorized all 11 prescription medications found in Smith's hotel room the day she died.

Eroshevich had traveled with Smith to Florida.

More than 600 pills, including 450 muscle relaxants, were missing from prescriptions that were no more than five weeks old, according to the documents obtained by The Associated Press through a public records request.

California's medical board also opened an inquiry to determine if there was any misconduct by Kapoor.

Methadone is a popular narcotic painkiller that is used as part of drug addiction detoxification and maintenance programs. Methadone overdoses can cause shallow breathing and dangerous changes in heart beat.

A lawyer for Stern has said she took the sleeping aid to cope with grief over the death of her son Daniel, 20, in the Bahamas.

Smith gave birth to daughter Dannielynn in September 2006, a few days before the death of her son.

Stern initially claimed to be Dannielynn's father, but Smith's ex-boyfriend Larry Birkhead eventually showed he was the father and is now raising the child.

The baby could inherit millions from the estate of Smith's late husband, Texas oil tycoon J. Howard Marshall II. A judge has appointed Birkhead guardian of the estate.

California Attorney General Brown said his office was cracking down on the abuse of legal drugs.

"Prescription drugs are abused in far too many cases," he said. "I want people to know that henceforward, the DOJ will be on the trail of people who abuse dangerous but lawful drugs."

FOX News' Catherine Donaldson-Evans, Ian McCaleb and The Associated Press contributed to this report.