The results of Philip Seymour Hoffman's autopsy were inconclusive, a spokesperson for the New York City Medical Examiner's office confirmed to E! News on Wednesday, Feb. 5.
Additional tests, including a toxicology study, must be conducted in order to determine what caused the actor's death. There is no timetable as to when the other test results will be released.
Hoffman's body was discovered on the bathroom floor in his New York City apartment after an apparent drug overdose on Sunday, Feb. 2. He was 46.
Investigators have since found more than 50 envelope bags of heroin at Hoffman's apartment, as well as several empty bags, syringes and prescription medications.
Meanwhile, the New York City Police Department has confirmed that four people have been arrested as part of its ongoing investigation into Hoffman's death.
Officers searched three apartments on the 300 block of Mott Street on Tuesday, Feb. 4. They arrested three men and one woman and recovered 350 glassine-type bags of what is believed to be heroin. All four are scheduled to be arraigned on Wednesday afternoon in Manhattan Criminal Court.
Hoffman had struggled with addiction problems in the past, and sought treatment for abusing heroin in May 2013.
A rep for the late actor confirmed to E! News that a private funeral will be held in New York City for family and close friends, adding that a separate memorial service is also in the works for later this month.
—Reporting by Lindsay Good