02/06/2008 at 04:10 PM EST
With the autopsy results for Heath Ledger
now a matter of public record
, the federal government is stepping in to determine how the actor was able to obtain so many prescription drugs.
"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 tells PEOPLE, confirming news first reported by TVGuide.com
New York City's Chief Medical Examiner on Wednesday announced
that the 28-year-old actor's Jan. 22 death was accidentally caused by "the combined effects of Oxycodone, Hydrocodone, Diazepam, Temazepam, Alprazolam, and Doxylamine."
said the Drug Enforcement Administration would probe how Ledger obtained the various drugs. Oxycodone is a painkiller, Hydrocodone is also known as Vicodin, Diazepam is commonly called Valium, Temazepam treats anxiety or sleeplessness, Alprazolam is known as Xanax, and Doxylamine is a sedating antihistamine often used as a sleep aid.
– Kathy Ehrich Dowd, Nicole Weisensee Egan and Stephen M. Silverman