Story highlights "This just shouldn't be," actor Robert DeNiro says

Philip Seymour Hoffman described his struggles with addiction in 2011 "60 Minutes" interview

Police are investigating the scene; an autopsy is scheduled for Monday

Law enforcement sources tell CNN that a needle was found in Hoffman's arm

Oscar-winning actor Philip Seymour Hoffman was found dead in his Manhattan apartment Sunday of an apparent drug overdose, law enforcement sources said.

Police said Hoffman, 46, was found on the bathroom floor and pronounced dead at the scene. Investigators found two bags of what is believed to be heroin inside the fourth-floor apartment, law enforcement officials said.

"We are devastated by the loss of our beloved Phil and appreciate the outpouring of love and support we have received from everyone. This is a tragic and sudden loss and we ask that you respect our privacy during this time of grieving," Hoffman's family said in a statement. "Please keep Phil in your thoughts and prayers."

Hoffman was last seen alive at 8 p.m. Saturday, a law enforcement official said. He was expected to get his children on Sunday, but didn't show up, the official said. Playwright David Katz and another person went to the apartment and found him dead, the official said.

JUST WATCHED Movie star Philip Seymour Hoffman dies Replay More Videos ... MUST WATCH Movie star Philip Seymour Hoffman dies 03:06

JUST WATCHED Philip Seymour Hoffman's memorable scenes Replay More Videos ... MUST WATCH Philip Seymour Hoffman's memorable scenes 01:18

JUST WATCHED See one of Hoffman's last interviews Replay More Videos ... MUST WATCH See one of Hoffman's last interviews 03:43

JUST WATCHED Writer: Hoffman got under your skin Replay More Videos ... MUST WATCH Writer: Hoffman got under your skin 02:09

A needle was in the actor's left arm, and eight empty glassine-type bags that usually contain heroin were found in the apartment, law enforcement sources told CNN.

The bags were stamped with "Ace of Hearts" and "Ace of Spades" -- street names for the heroin, the sources said.

Hoffman loved 'deep, dense characters'

Hoffman won an Academy Award for best actor for the 2005 biopic "Capote" and drew critical acclaim for his roles in a wide variety of films.

He was a beefy 5-foot-10-inch man, but was convincing as the slight, 5-foot-3-inch Truman Capote. He had a booming voice like a deity's but often played shlubby, conflicted characters.

"He just loved those deep, dense characters. That's where I think he found his true calling," said Bradley Jacobs, a senior editor of Us Weekly.

In Hollywood, Hoffman's big break came with a small role as Chris O'Donnell's classmate in the 1992 film "Scent of a Woman."

For years, Hoffman was the kind of anonymous character actor who earned critical raves but was often unnoticed by the general public. He used his abilities to take chances with such directors as a then-unknown Paul Thomas Anderson, with whom he worked in "Hard Eight" (and several ensuing films, as both became better known) and Todd Solondz ("Happiness").

"I think about that a lot," he told Esquire in 2012 of his anonymity. "I feel it cracking lately, the older I'm getting. I think I'm less anonymous than I was."

As an actor, Hoffman could be heartfelt and giving, as with his male nurse in "Magnolia" or rock critic in "Almost Famous," or creepily Machiavellian, like the gamemaster in the latest "Hunger Games" movie or a "Mission: Impossible" movie villain.

He also appeared in "Charlie Wilson's War," "Doubt," and "The Master," for which he was nominated as best supporting actor.

He appeared last month at the Sundance Film Festival, where a movie he starred in, "God's Pocket," premiered.

"He seemed really in good spirits, and it's just so shocking," said CNN Entertainment Commentator Krista Smith, who interviewed Hoffman at the festival. "Because, just looking at his body of work and knowing how many actors revered him and how they look up to him. ... The one thing that was so special about him is that he crossed all platforms ... Every genre, he managed to fit in and just be brilliant at whatever he was doing."

Beloved resident of New York neighborhood

Philip Seymour Hoffman arrives for the Los Angeles premiere of 'The Hunger Games: Catching Fire' at the Nokia Theatre LA Live in Los Angeles, California, on November 18.

Photos: Philip Seymour Hoffman in his own words Photos: Philip Seymour Hoffman in his own words Hide Caption 1 of 7 Photos: Philip Seymour Hoffman in his own words Hide Caption 2 of 7 Photos: Philip Seymour Hoffman in his own words Hide Caption 3 of 7 Photos: Philip Seymour Hoffman in his own words Hide Caption 4 of 7 Photos: Philip Seymour Hoffman in his own words Hide Caption 5 of 7 Photos: Philip Seymour Hoffman in his own words Hide Caption 6 of 7 Photos: Philip Seymour Hoffman in his own words Hide Caption 7 of 7

But despite his love of performance, Hoffman was a private person who rarely spoke about his family, Jacobs said.

In New York's Greenwich Village neighborhood where he lived, it was common to see the actor riding a bicycle and walking his children to the public school they attended.

"He'd go quietly about his business with his children. I still remember the day he won the Oscar, him walking his kids to school, not long after. And people were giving him high fives," said CNN's Rose Arce, whose daughter attended school with Hoffman's children. "It looked like it really meant something to him to have his neighbors saying congratulations. It's shocking, and I know everyone in the neighborhood is going to feel like they're missing a friend, like a friend has died."

After his Oscar win at the Academy Awards in 2006, Hoffman thanked his mother for taking him to his first play.

"She brought up four kids alone and she deserves a congratulations for that. ... And she took me to my first play and she stayed up with me and watched the NCAA Final Four, and my passions, her passions became my passions. And, you know, be proud, Mom, because I'm proud of you and we're here tonight and it's so good," he said in his acceptance speech.

Hoffman's father was a salesman and his mother was a family court judge, a biography on the Turner Classic Movies website says. He landed his first professional stage role before graduating from high school and went on to study acting at New York University.

Hoffman stayed active on stage even as his star rose in Hollywood. He starred in a Broadway production of "Death of a Salesman" in 2012 and was co-artistic director of the Labyrinth Theater Company in New York.

He is survived by three children and his longtime partner, Mimi O'Donnell.

Battling addiction

Last year Hoffman revealed that he had entered rehab to deal with a drug problem, telling TMZ that he'd kicked a substance abuse habit for 23 years but recently relapsed.

In a 2011 interview with "60 Minutes," he discussed his past struggles with drug and alcohol addiction.

"Anything I could get my hands on, I liked it all," he said.

Asked why he decided to sober up, he replied, "You get panicked. ... I was 22 and I got panicked for my life, it really was, it was just that. And I always think, 'God, I have so much empathy for these young actors that are 19 and all of a sudden are beautiful and famous and rich.' I'm like, 'Oh my God. I'd be dead.'"

According to TMZ, Hoffman said last year that he'd fallen off the wagon, started taking prescription pills and slipped into snorting heroin.

The actor's public comments about his battle with substance abuse illustrate the struggles many addicts face, according to HLN's Dr. Drew Pinsky, an addiction specialist.

"Someone with opiate addiction, they are doing pushups their whole lives. And they must work on it all the time. And even working on it, there's a high probability of relapse. And God willing, they get adequate treatment, and they re-engage in treatment, and things go well," Pinsky said. "But often, it's a frequently fatal condition. We just simply have to continually remind ourselves of that. And now it has taken a glorious, glorious talent from us."

After he returned from rehab, Hoffman rented the apartment where his body was found Sunday, two neighbors said. The rest of his family lived elsewhere in the neighborhood.

'He was a giant talent'

Word of Hoffman's death sparked a flood of reactions from actors, directors, studio heads and fans.

"This is a horrible day for those who worked with Philip," actor Tom Hanks said in a statement. "He was a giant talent. Our hearts are open for his family."

Lionsgate, the studio behind "The Hunger Games" movies, described Hoffman as "a singular talent and one of the most gifted actors of our generation."

In a Twitter post, actor Jim Carrey described Hoffman as a "beautiful soul."

"For the most sensitive among us the noise can be too much," he wrote. "Bless your heart."

Robert DeNiro, who starred opposite Hoffman in the 1999 movie "Flawless," said he was "very, very saddened" by Hoffman's death.

"This is one of those time where you say 'this just shouldn't be. He was so young and gifted and had so much going, so much to live for.'"

For Mike Nichols, who directed Hoffman in his Oscar-nominated turn in "Charlie Wilson's War," there were no words, just grief.

"No words for this. He was too great and we're too shattered," he said in an e-mailed statement.

Police investigating

As fans and neighbors gathered outside the apartment building where Hoffman was found, police were combing his apartment for evidence Sunday. As part of the investigation, authorities are looking into whether anyone was with the actor when he died, law enforcement officials said.

An autopsy will be conducted on Hoffman's body Monday, said Julie Bolcer, a spokeswoman for New York City's Office of Chief Medical Examiner.

Law enforcement sources told CNN that detectives will track Hoffman's recent activities to see where he purchased what appears to be heroin.

Moving on the theory that Hoffman's death was a drug overdose, they'll now try to seek exactly where he bought it, the sources said.

This will involve searching his phone and trying to track some of his movements, the sources told CNN.

A federal law enforcement official said the "Ace of Hearts" and "Ace of Spades" stamps on the bags are familiar to law enforcement. They're among hundreds of stamps drug distribution crews use to brand their products.

Heroin use on the rise, authorities warn

Authorities have warned that heroin addiction is soaring and noted an uptick in the availability of the drug.

Last week the Drug Enforcement Administration announced a heroin mill bust in the Bronx, New York, after they seized $8 million worth of the drug.

The DEA has warned that people who are addicted to opioid prescription pills are now finding highly pure heroin easier and cheaper to obtain.

It produces a similar, if more dangerous, high because unlike the pills, there is no way to regulate the dosage of heroin, given the undetermined purity.

That's why investigators likely won't have to look far to find where Hoffman could get the drug, Pinsky said.

"It's right outside his house, I guarantee you," he said, "or somewhere nearby."