LOS ANGELES -- Investigators are focusing on at least five doctors who prescribed drugs to Michael Jackson as they try to unravel the circumstances surrounding pop star's death, according to law enforcement sources.

Authorities removed drugs and other medical evidence from the Los Angeles mansion where Mr. Jackson was stricken and are trying to determine whether the medications were prescribed properly and whether they played any role in his death.

Some of the prescriptions were made out in the name of Jackson pseudonyms, and in some cases, the drugs had no prescription labels on them at all, the sources told the Los Angeles Times.

One of the most tantalizing clues so far is the discovery of what one source described as "numerous bottles" of the powerful sedative Diprivan at the home. The source, who spoke on the condition of anonymity because it was an ongoing investigation, said some of the bottles were full and other were empty. None bore prescription labels, and investigators are trying to determine how Mr. Jackson got the drugs.

Diprivan is an extremely potent drug that is supposed to be administered by a person trained to administer anesthesia, such as an anesthesiologist or a certified registered nurse anesthetist--typically in a hospital. Experts expressed alarm that it would be used at a private home.

"It's a very dangerous drug if self-administered or administered by someone not trained in airway management and cardiac life support," said Ethan Bryson, an assistant professor of Anesthesiology at Mount Sinai School of Medicine in New York. "You need to have someone who knows what they are doing when they administer it."

Diprivan, the market name for propofol, is one of the most widely used IV drugs for general anesthesia. The product label from U.S. Food and Drug Administration says a patient being given the drug should be monitored at all times for early signs of abnormally low blood pressure, low oxygen levels and stopped breathing. Problems with the heart or breathing are more likely to occur following rapid administration of the drug. The label states that equipment to provide artificial ventilation, supplemental oxygen and CPR "must be immediately available."

It's unclear whether any of this equipment was found at Mr. Jackson's home.

Abuse of Diprivan is a growing problem, said Dr. Paul Wischmeyer, an anesthesiologist at the University of Colorado.

Dr. Wischmeyer is co-author of a 2007 study of Diprivan abuse in the journal Anesthesia & Analgesia. The study found that in an e-mail survey of 126 academic anesthesiology training programs nationwide, 18 percent of departments reported one or more incidents of Diprivan abuse in the previous 10 years. Of the 25 individuals who abused propofol, seven died as a result of the drug abuse, including six who were residents, according to the journal study.

"A lot of people do it because it makes you completely blotto. It totally takes away all anxiety, all fear," Dr. Wischmeyer said. "It's incredibly relieving of pain anxiety and stress. People do it to escape."

It remains unknown whether prescription drugs played any role in Mr. Jackson's death. The L.A. County Coroner's office is awaiting the results of toxicology test before listing a cause of death.

The coroner and Los Angeles Police Department are being aiding in their probe by the Drug Enforcement Administration and California Attorney General's office. Both agencies have expertise in investigating doctors suspect of improperly prescribing drugs.

The attorney general's office investigated two doctors who were charged earlier this year with repeatedly supplying model Anna Nicole Smith with addictive prescription drugs in the years before she died. The DEA is expected to investigate whether doctors who prescribed medication had a "face to face" relationship with Mr. Jackson and provided a proper diagnosis, which is required by law.

Diprivan first surfaced in the Jackson case last week when a nurse, Cherilyn Lee, said that the pop star sought the drug from her earlier this year. Ms. Lee said Mr. Jackson was troubled about having insomnia and asked her to get some Diprivan for her.

Ms. Lee said she told Mr. Jackson, "This medication is not safe."

She said she never saw him take the drug.