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As family, friends and fans mourn the death of Philip Seymour Hoffman, new details about the actor's apparent drug overdose emerged Monday.

The Oscar-winning actor, 46, was discovered dead in a New York City apartment just after 11:30 a.m. Sunday, with a syringe still in his arm, authorities said. Law enforcement officials told NBC News that authorities at the scene found 49 full bags of heroin, 23 empty bags of heroin, four bags of white powder believed to be cocaine, as well as various prescription drugs.

Officials also discovered books about Truman Capote, the legendary author whom Hoffman played, in an Academy Award-winning performance, in the eponymous 2005 film.

The two labeled “brands” of heroin found in the apartment — “Ace of Spades” and “Ace of Hearts” — tested positive for heroin, although more sophisticated tests that will confirm the purity of the drug are still ongoing.

A law enforcement official told NBC News that toxicology tests, which could take a few days to complete, will likely determine the actor’s cause of death. It was unclear Monday if the heroin Hoffman had injected was tainted or if he took too much of the drug.

Multiple law enforcement sources told NBC News that authorities found six bottles of prescription drugs — including the blood pressure medication clonidine hydrochloride; the addiction treatment drug buprenorphine; the attention-deficit disorder treatment drug vyvanse; the anti-anxiety drug hydroxyzine; and the muscle relaxer methocarbamol.

Hoffman had spoken openly about past substance abuse battles, saying he quit using drugs and alcohol and "got sober" at 22 years old.

But in early 2013, Hoffman checked himself into rehab for 10 days. He told TMZ that he had begun using prescription medicines, and his use escalated to heroin.

In addition to his win for “Capote,” Hoffman was nominated three times for Oscars for his supporting roles in “Doubt,” “Charlie Wilson’s War,” and “The Master.”

The marquees of Broadway theaters in New York will be dimmed in his memory Wednesday night, the Broadway Press League said in a statement. Hoffman was a three-time Tony Award nominee for his performances in "Death of a Salesman," "True West" and "Long Day's Journey into Night."

Daniel Arkin of NBC News contributed to this report.