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Federal drug investigators have taken over the inquiry into the January 22 death of actor Heath Ledger in a New York apartment, a law enforcement source told CNN Thursday.

Ledger, 28, an Oscar-nominated Australian actor, died of an accidental overdose of six types of medication, according to the New York City medical examiner's office.

The medical examiner's office said Ledger "died as the result of acute intoxication by the combined effects of oxycodone, hydrocodone, diazepam, temazepam, alprazolam and doxylamine." Read full article »

CNN's Brian Vitagliano contributed to this report.

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