Medical examiners' spokeswoman Julie Bolcer said there was no timetable for the autopsy to be finished. She declined to discuss the pending tests, but toxicology and tissue tests are typically done in such cases.
While awaiting the official findings on the cause and manner of the Academy Award-winning actor's death, police have been investigating it a suspected drug overdose.
Hoffman, 46, was found dead Sunday with a needle in his arm, and tests found heroin in samples from at least 50 packets in his apartment in Manhattan's Greenwich Village, law enforcement officials have said. Authorities have been testing whether the drug was mixed or tainted with anything else. An official said authorities also found unused syringes, a charred spoon and various prescription medications, including a drug used to treat heroin addiction, a blood-pressure medication and a muscle relaxant.
The officials spoke on condition of anonymity because they weren't authorized to talk about the evidence found.
Hoffman had been frank about struggling with substance abuse. He told 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'd 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."
Officials have been gathering pieces of the puzzle of what Hoffman was doing in the days and hours before his body was found, in his bathroom, around 11:30 a.m. the next day by his assistant and one of his friends. The friend had spoken to the actor by phone around 9 p.m. Saturday, a law enforcement official said.
His death came amid rising concern around the region about a powerful drug hybrid - mixtures of heroin and fentanyl, a synthetic form of morphine - that has been linked to deaths in other states, including 22 deaths within a week last month in western Pennsylvania. But the drug found at Hoffman's apartment tested negative for fentanyl, a police official said.
Associated Press writer Jennifer Peltz contributed to this report.