Autopsy results for Heath Ledger released Wednesday confirm that the actor died from an accidental overdose of a mixture of prescription drugs; New York’s Drug Enforcement Administration will initiate an investigation to determine whether any of the pills were prescribed illegally.

The New York City medical examiner’s officer announced Wednesday that Heath Ledger’s death was caused by an accidental “abuse of prescription medications.”

“Mr. Heath Ledger died as the result of acute intoxica- tion by the combined effects of oxycodone, hydrocodone, diazepam, temazepam, alprazolam and doxylamine,” the medi- cal examiner's spokeswoman, Ellen Borakove, said in a written statement. “We have concluded that the manner of death is accident, resulting from the abuse of prescription medications.”

An autopsy performed a day after the actor’s death was inconclusive and further toxicology tests were conducted. Ledger was found dead in his New York apartment on Jan. 22 by a masseuse; investigators found sleeping pills near his bed and other prescription drugs around the apartment. He was only 28.

The six medications identified by the medical examiner are prescribed for a number of conditions: oxycodone is a painkiller; hydrocone is generically known as Vicodin, also a painkiller; diazepam, commonly called Valium, and alprazolam, also known as Xanax, are antianxiety medications; temazepam treats anxiety and sleeplessness; while doxylamine is an antihistamine commonly used as a sleeping aid.

Separately, the medications are generally safe and effective; combined, their effect can be fatal, medical experts said.

New York’s Drug Enforcement Administration will investigate how the late actor obtained all the pills, as no doctor would have likely prescribed such a combination of painkillers, antianxiety drugs and sleeping medication.

“We are working with the NYPD to identify any illegally prescribed drugs that may have been prescribed to [Ledger],” New York's Drug Enforcement Administration spokesman Erin Mulvey told People magazine Wednesday.

TVGuide.com reported on Wednesday that the DEA has requested copies of the Australian actor’s autopsy as well as the original police report from the crime scene.

Heath Ledger’s family, as well as former fiancée Michelle Williams and the couple’s two-year-old daughter Matilda, arrived in Perth, Australia, the actor’s hometown, earlier this week. A private funeral is expected to take place this Saturday. Ledger will be buried in the family plot, near his grandparents, at Perth's Karrakatta Cemetery, according to media reports.