Investigators discovered close to 50 envelopes of what they believed was heroin in the apartment, the law enforcement sources said. They also found used syringes, prescription drugs and empty bags that authorities suspect are used to hold heroin, the sources said.
Preliminary tests Tuesday showed the heroin recovered from the apartment does not contain fentanyl, a law enforcement official told CNN.
More testing will be done, but as of now no fentanyl has been detected.
Fentanyl is a powerful narcotic used to treat cancer patients' pain.
Last week, Maryland officials said heroin tainted with fentanyl had claimed at least 37 lives since September. And last month, at least 22 people died after using heroin mixed with fentanyl in western Pennsylvania.
Hoffman revealed last year that he had entered rehab to deal with a drug problem, telling TMZ that he'd kicked a substance abuse habit for 23 years.
In a 2011 interview with "60 Minutes," he discussed his past struggles with drug and alcohol addiction.
"Anything I could get my hands on, I liked it all," he said.
Fear, Hoffman said, made him sober up.
"You get panicked. ... I was 22 and I got panicked for my life, it really was, it was just that," he said. "And I always think, 'God, I have so much empathy for these young actors that are 19 and all of a sudden are beautiful and famous and rich.' I'm like, 'Oh my God. I'd be dead.'"
Last year, Hoffman said he'd fallen off the wagon, started taking prescription pills and slipped into snorting heroin, according to TMZ.
Magazine writer John Arundel said he met the actor at the Sundance Film festival in Utah two weeks before his death.
"I said, 'what do you do? And at that point, he took off his hat and he said, 'I'm a heroin addict,' " Arundel said. "Didn't look like he was (joking). Seemed like he was having one of those 'coming to God' moments- where it just stuck him as, 'this is the revelatory moment.'"
Family and close friends of the actor will hold a private funeral service in New York. Plans are also under way for a memorial service later this month. No information on the dates was available.