Philip Seymour Hoffman's Autopsy Results Inconclusive

The investigation into Philip Seymour Hoffman's death continues.

On Wednesday afternoon, it was announced that the actor's autopsy results were inconclusive. An official cause of death won't be determined until further studies are conducted, including a toxicology report, "The Insider With Yahoo" confirmed.

This is fairly standard as medical examiners can't make final determinations until they know all the substances that were in Hoffman's body, especially considering the nature of his death, having been found dead with a syringe in his arm on Sunday and 50 packages of what police believe to be heroin in his Manhattan rental apartment. Further, it could take a couple weeks until the official findings are announced.

On Tuesday night, four people — three men and a woman — were arrested on narcotics charges Tuesday in Manhattan and questioned about a possible link to the heroin, "The Insider With Yahoo" has confirmed. According to CBS, more than 350 bags of the drug were found in the three apartments that were searched, but none of them had the "Ace of Spades" logo on the bags similar to some recovered among the "Hunger Games" star's belongings.

[Related: Philip Seymour Hoffman's Life as a New Yorker: 'He Was Just Phil']

The NYPD is trying to piece together Hoffman's final hours. It was determined that the Oscar winner, who was found dead on the floor of his bathroom Sunday with a syringe in his arm, made six ATM transactions totaling $1,200 at a local grocery store the night before he was found dead.

A police official did tell the news station that the heroin recovered at Hoffman's apartment was tested and did not contain the powerful additive fentanyl, which has been linked to numerous heroin deaths recently.

Meanwhile, Hoffman's partner, Mimi O'Donnell, is making funeral preparations. On Tuesday, she released a statement announcing a private funeral service — which is expected to take place Friday — in Manhattan for family and close friends. There will be a memorial service later this month, also in New York City.

"The family wishes to thank everyone for their continued support and good wishes," said the statement, which also asked that donations "be made in Phil’s name to two charities that were very close to his heart: The DreamYard Project and the Christopher and Dana Reeve Foundation.

[Related: 'Hunger Games' Release Dates Won't Be Affected by Philip Seymour Hoffman Loss]

O'Donnell, who has three young children with Hoffman, has received a steady stream of visitors in their family home, which is a few blocks from his rental apartment, following his death. After Cate Blanchett and Justin Theroux stopped by Monday, Joaquin Phoenix, Ethan Hawke, and Bobby Cannavale were spotted visiting as well.

Hoffman had a long-time struggle with drugs and alcohol. He had said he first went to rehab and got sober when he was 22. After a period of sobriety, he relapsed last year and did a second 10-day stint in rehab last April.