Celebrity website TMZ obtained details on prescription drugs contained in an investigator's report, which was meant to be confidential.
Assistant Chief Coroner Ed Winter said: "I'm furious, we don't normally release partial information - if partial information goes out, it of course makes us look bad, everybody ought to get it at the same time."
Brittany, 32, died on Sunday after collapsing at her Hollywood Hills home. Police and the coroner's office are investigating the death, but detectives have said their initial inquiry found no evidence of wrongdoing.
TMZ's report stated the investigator, who is only identified by last name, noted numerous bottles of prescription medications were found in the actress's name at the home where she collapsed.
Winter said he spoke with TMZ's managing editor, Harvey Levin, who declined to say how the site obtained details from the report. Winter said Levin told him it did not come directly from the investigator or the office's two main press contacts, which includes Winter.
An autopsy on Brittany was completed on Monday and a determination on her cause of death has been deferred until toxicology and tissue testing are complete. Her death may be from natural causes, but that won't be decided until all testing is complete, Winter said.
Winter added he was concerned about other information about Brittany's death being released before his office releases its conclusions in four to six weeks.
"The investigator did interview her doctor," Winter said. "I haven't even seen what was obtained from the doctor. I'm worried that TMZ or somebody else got that info."
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