Last Updated Feb 28, 2014 5:22 PM EST
Philip Seymour Hoffman died from a toxic mix of heroin and other drugs, officials said Friday.
A spokeswoman for the New York City medical examiner said that the Oscar-winning actor died of "acute mixed drug intoxication," including heroin, cocaine, amphetamines and benzodiazepines, which are psychoactive drugs.
The death was ruled an accident.
Benzodiazepines and heroin are depressants, and can slow respiration and lower blood pressure to dangerous levels. Uppers like cocaine and amphetamine and cause irregular heart rates and rhythm, explained CBS News chief medical correspondent Dr. Jon LaPook.
"This is an astonishingly dangerous combination of drugs," he added. "Together, it's just so dangerous -- it's not surprising that they led to his very very sad demise."
Police had been investigating his death as a suspected drug overdose. An autopsy in February was inconclusive and medical examiners said more tests were needed.
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.
Law enforcement officials have said Hoffman was found dead on Feb. 2 with a needle in his arm, and tests found heroin in samples from at least 50 packets in his Manhattan apartment.
Hoffman, 46, who won an Oscar for "Capote" and starred in numerous other movies as well as New York stage productions, 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.
His will bequeaths all of his personal property to Mimi O'Donnell, the mother of his three children.
Investigators have been probing how Hoffman may have obtained the heroin. Tests of the heroin in his apartment have found that it was not cut with a dangerous additive such as fentanyl, a synthetic form of morphine used to intensify the high that has been linked to deaths in other states.
A musician, veteran jazz player Robert Vineberg, has been charged with keeping a heroin stash in a lower Manhattan apartment amid the investigation into Hoffman's death. Vineberg, who has said he was a friend of the Tony Award-nominated Hoffman, hasn't been charged in Hoffman's death and has said he didn't sell him the heroin found in his apartment.
As police followed a tip after Hoffman's death, they said they found about 300 small bags of heroin, worth about $10 apiece on the street, and $1,300 in cash in Vineberg's apartment and music studio.