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The Los Angeles County Coroner's office subpoenaed Michael Jackson's dermatologist on Tuesday seeking "additional medical records" from the physician's Beverly Hills office, officials said.
Coroner's chief Craig Harvey confirmed reports that assistant chief Ed Winter served the subpoena at the office of doctor Arnold Klein, but did not provide any further information.
The development comes as investigators scrutinize the possible role of drugs in the death of Jackson, 50, who died on June 25 after suffering an apparent cardiac arrest at his home in Los Angeles.
Last week Klein denied giving Jackson a dangerous sedative -- Diprivan -- discovered at the superstar's rented mansion.
Diprivan is used to induce unconsciousness in hospital patients ahead of major surgery and experts say it should only be administered by a trained anesthesiologist.
Klein told CNN he was aware Jackson had used the drug in the past but said he had never given the singer the substance.
"I knew at one point he was using Diprivan when he was on tour in Germany," Klein said. "He was using it with an anesthesiologist to go to sleep at night and I told him he was absolutely insane."
Los Angeles coroners have deferred issuing a cause of death in Jackson's case until the results of exhaustive toxicology tests are known.
