NEW YORK – Tests have confirmed that there was heroin in at least some of the scores of plastic packets in the apartment where actor Philip Seymour Hoffman was found dead, a law enforcement official said Monday, and authorities are working to determine whether the drug was mixed or tainted with anything else.

Medical examiners have not made an official determination of the cause of the actor’s death, but police have been investigating it as a suspected overdose. Hoffman 46, was found in a bathroom with a syringe in his arm, law enforcement officials have said.

A few details have begun to sketch a picture of his final day and the circumstances in which he was found in his apartment in Manhattan’s Greenwich Village on Sunday. And questions have swirled about whether the death of the Academy Award winner could be linked to a potent blend of heroin and synthetic morphine that has been tied to deaths elsewhere, though there are no official findings pointing to that scenario.

“The direction of the investigation is going to depend, in large part, on the findings of the medical examiner and the findings of the lab tests,” chief police spokesman Stephen Davis said.

An autopsy was conducted Monday, but results weren’t expected until at least today.

A friend had spoken to Hoffman by phone at about 9 p.m. Saturday. It was the last time that investigators are aware of anyone having contact with him, a law enforcement official said. The official said the actor’s door was double-locked when his body was found at about 11:30 a.m. the next day by the friend and Hoffman’s assistant.

In the apartment were at least four dozen small packets variously stamped with the ace of hearts and others with the ace of spades, two law enforcement officials said Monday. Tests showed heroin in each type, one of the officials said.

Authorities also found unused syringes, a charred spoon and various prescription medications, including a blood-pressure drug and a muscle relaxant, one of the officials said.

Stamps are common as a form of branding in the drug world, and authorities make note of the ones they encounter, though they’re hardly trademarks – different producers might use the same symbol.

The Buffalo News, in a special report published Sunday, the day Hoffman’s body was found, noted that concern has risen in recent months about fentanyl, a synthetic morphine substitute roughly 100 times more powerful than morphine, being mixed with or substituted for heroin. It’s unclear whether the drugs found in Hoffman’s apartment contained fentanyl.

The News also reported that there is a heroin epidemic in Erie County, with 29 people having died of heroin overdoses in 2013, almost a third more than the year before.

In western Pennsylvania, 22 people died within a week last month from suspected overdoses of heroin and fentanyl, authorities said last week.

On Long Island, the Nassau County Medical Examiner’s Office is probing at least five deaths involving fentanyl being sold in packets stamped “24K.”