Two doctors suspected of supplying medications to Heath Ledger are under investigation by federal drug authorities, DEA sources tell ABC News.

Doctors in Texas and California are being questioned to determine whether the medications for Ledger — who died Jan. 22 from a lethal combination of painkillers, sleeping pills and anti-anxiety drugs — were improperly prescribed.

On Feb. 6, the spokeswoman for the New York City medical examiner's office said Legder "died as the result of acute intoxication by the combined effects of oxycodone, hydrocodone, diazepam, temazepam, alprazolam and doxylamine." Ledger took "prescribed therapeutic doses...or less" of each medication he ingested, however, the medications were not meant to be taken together, according to the ME's office. The death was ruled an accident.