NEW YORK >> Four people were taken into custody on drug charges after police investigating the death of actor Philip Seymour Hoffman executed search warrants at several New York City apartments, two people with knowledge of the investigation said today.

A confidential source provided a tip that the suspects may have supplied Hoffman drugs, according to the people, who spoke to The Associated Press on the condition of anonymity because investigators have not obtained evidence to corroborate the reported connection.

Police say undisclosed quantities of heroin and marijuana were found Tuesday night in the three apartments in a lower Manhattan building. The four suspects — three of whom live in the building — face charges of criminal possession of a controlled substance. Two also face charges of criminal use of drug paraphernalia.

Hoffman was found dead over the weekend in his Greenwich Village apartment with a syringe in his arm.

The NYPD’s intensive effort to determine the source of the drugs in an apparent accidental overdose is unusual. Courts have found that under state law, drug dealers cannot be held liable for a customer’s death.

A police official said Tuesday that heroin recovered at the Oscar-winning actor’s apartment after he was found dead tested negative for the powerful additive fentanyl.

Samples taken from Hoffman’s apartment didn’t contain the potent synthetic morphine, which is added to intensify the high and has been linked to 22 suspected overdose deaths in western Pennsylvania, said the official, who wasn’t authorized to talk about the evidence and insisted on anonymity.

Investigators also determined that the “Capote” star made six ATM transactions for a total of $1,200 inside a supermarket near his home the day before his death, law enforcement officials said Tuesday. They’ve been piecing together his final hours using video surveillance to determine his whereabouts.

The 46-year-old was found dead in his bathroom Sunday. His door was double-locked when his body was found around 11:30 a.m. by his assistant and a friend, law enforcement officials have said.

Besides the bank records, investigators discovered buprenorphine, a drug used to treat heroin addiction, at Hoffman’s apartment and are examining a computer and two iPads found at the scene for clues, two law enforcement officials said.

Police have said the medical examiner’s ruling on his cause of death will determine whether there is any criminality but they suspect it was an overdose. No official determination has been made yet.

More than 50 small plastic envelopes of heroin were recovered in Hoffman’s apartment along with syringes, a charred spoon and various prescription medications, including a blood pressure drug and a muscle relaxant, law enforcement officials have said.

Some of the packets were variously stamped with the ace of hearts and others with the ace of spades, they said.

Addiction specialist Dr. Louis Baxter, a former president of the American Society of Addiction Medicine, said addicts, especially those who have built up high tolerances, can use as much as two bundles of heroin, or about two dozen packets, per day.

“Addicts with financial means will actually stockpile their drug,” he said. “Someone who has developed tolerance, who is seeking to develop a high, may need to inject every two hours or so.”

The Frank E. Campbell Funeral Home, which has orchestrated the funerals for celebrities including Jacqueline Kennedy Onassis and James Cagney, said Hoffman’s family has requested a private funeral. It will be held Friday.

___

Associated Press writers Jake Pearson and Jennifer Peltz contributed to this report.