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Four people have been taken into custody on drug charges after police investigating Philip Seymour Hoffman's death executed search warrants.
The medical examiner's office, meanwhile, says more tests are needed to determine what killed him.
There was no timetable for Hoffman's autopsy to be finished, said medical examiner office spokeswoman Julie Bolcer, who declined to discuss the pending tests.
Toxicology and tissue tests are typically done in such cases.
Police have been investigating Hoffman's death as a suspected drug overdose.
The Oscar-winning actor was found dead on Sunday (Monday morning, NZT) with a needle in his arm.
Tests found heroin - but no traces of the potent synthetic morphine additive fentanyl, which is added to intensify the high and has been linked to 22 suspected overdose deaths in western Pennsylvania - in samples from at least 50 packets in his apartment in Manhattan's Greenwich Village, law enforcement officials have said.
The four people were taken into custody on Tuesday night after police executed search warrants at several New York City apartments, based on a tip provided by a confidential source that the suspects may have supplied Hoffman with drugs, according to two people with knowledge of the investigation who spoke on the condition of anonymity.
Police say undisclosed quantities of heroin and marijuana were found on Tuesday night in three apartments in a lower Manhattan building.
The four suspects - three of whom live in the building - face charges of criminal possession of a controlled substance. Two also face charges of criminal use of drug paraphernalia. They're awaiting arraignment in Manhattan Criminal Court.
Investigators have determined that the "Capote" star made six ATM transactions for a total of $US1200 (NZ$1462) inside a supermarket near his home the day before his death, law enforcement officials have said.
Investigators have been piecing together Hoffman's final hours using video surveillance to determine his whereabouts. They're also examining a computer and two iPads found at the scene for clues.
The NYPD's intensive effort to determine the source of the drugs in an apparent accidental overdose is unusual. Courts have found that under state law, drug dealers cannot be held liable for a customer's death.
Hoffman had been frank about struggling with substance abuse, telling CBS' 60 Minutes in 2006 that had he used "anything I could get my hands on" before getting clean at age 22.
But in interviews last year, he said he had relapsed, had developed a heroin problem and had gone to rehab for a time.
Hoffman's relatives say they are devastated by a death both "tragic and sudden".
His funeral is scheduled for Friday.
Hoffman is survived by his partner, Mimi O'Donnell, and their three children.
A representative for Hoffman said the actor, who also appeared in such blockbusters as Twister and The Hunger Games, would be buried in a private memorial service, with a public memorial planned for later this month.