Several suspects were arrested on drug charges at a Manhattan building as investigators tried to determine whether they sold heroin to actor Philip Seymour Hoffman, who was found dead of an apparent overdose.

Two law enforcement sources said Hoffman's phone number was found on the cell phone of one of the suspects.

Three suspects -- Robert Vineberg, 57, Max Rosenblum and Juliana Luchkiw, both 22 -- were arrested on drug charges Tuesday after police searched three apartments in the Mott Street building and allegedly found about 300 bags of heroin stamped "Red Bull" and "Black List," along with three small bags of cocaine and some unidentified pills, according to NBC News.

A fourth suspect initially named by sources is not being charged because he does not live in the building and investigators cannot link him to the case, sources said.

All three suspects appeared before a judge Wednesday and entered not guilty pleas through their lawyers. They're being held until their next court appearance.

Luchkiw's lawyer, Stephen Turano, said his client had no relationship with Hoffman and that she was "in the wrong place at the wrong time." He said he believes the large amounts of recovered heroin were found in the other apartments.

Rosenblum and Luchkiw are a couple and live in the same apartment. Turano said only small amounts of cocaine and marijuana were recovered from their apartment, not heroin.

Police are looking into whether the suspects supplied drugs to Hoffman, who was found dead in the bathroom of his West Village apartment Sunday with a syringe in his arm, sources say. The Oscar-winning actor had been dead several hours when he was found by a friend and is suspected to have died of an overdose.

The medical examiner said Wednesday that the autopsy was inconclusive as to the cause and manner of death. Authorities are awaiting further test results, including toxicology.

Dozens of bags of heroin were found in Hoffman's apartment, along with prescription drugs and a bag of white powder police were testing for cocaine. Some of the heroin found there was stamped "Ace of Spades."

Hoffman's last known contacts on Saturday night were with his longtime girlfriend around 8 p.m., and a screenwriter friend about 9 p.m., officials said.

Sources say bank records show Hoffman withdrew $1,200 from an ATM at a supermarket near his West Village home between 8 p.m. and 9 p.m. the night he died. A witness told investigators he saw Hoffman speaking with two men wearing messenger bags as he withdrew the money.

Detectives are looking into whether he bought the drugs the night of his death.

Hoffman, who was 46 and had three children, won the Oscar for Best Actor in 2006 for his starring role in "Capote." He was nominated for Oscars three other times, including for 2012's "The Master," and he earned two Tony nominations for his work on Broadway.

Hoffman spoke over the years about past struggles with drug addiction. After 23 years sober, he admitted in interviews last year to falling off the wagon and developing a heroin problem that led to a stint in rehab.

--Katy Tur contributed to this story