The medical examiner's office said more tests are needed to determine what killed Philip Seymour Hoffman.
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 his death as a suspected drug overdose.
The Oscar-winning actor was found dead Sunday with a needle in his arm, and 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.
Investigators have determined that the "Capote" star made six ATM transactions for a total of $1,200 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. He told CBS' "60 Minutes" in 2006 that he had 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 said they were devastated by a death both "tragic and sudden."
Hoffman's co-stars George Clooney, Matt Damon and Bill Murray spoke about their friend from the red carpet at the world premiere of the historical drama 'The Monuments Men' in New York on Wednesday.
"Phil was awesome. Awesome. And generous. And, you know, one of those actors who was good enough for both of you — good enough that if you sucked, the scene would still be great, because he was in it," Damon said.
"He must have been in pain, you know. I'm glad that pain has ended for him, and I hope his family is OK," Murray said.
Hoffman's funeral is scheduled for Friday.
Associated Press writer Jennifer Peltz contributed to this report.