– After mass shootings this year, Americans are embroiled in a debate over the nature of the perpetrators and the factors that drive them.

Now, Hollywood is about to weigh in.

Screening at this year's Toronto International Film Festival was "Joker," and while it comes in the form of a comic book movie, it is the opposite of light. It addresses the question: What propels someone to pick up a gun and begin killing complete strangers?

"Set aside that it's the DC [Comics] universe," said Cameron Bailey, artistic director of the festival. "Just think of it as a great character study that goes really dark."

Warner Bros. brought the movie to the festival hoping to launch an award-winning run for a film that has become one of Hollywood's most closely watched and potentially explosive movies in years. The movie, which opens Oct. 4, is divisive, not just because of the traditional range of aesthetic opinions but because of what it represents and the speculation about which political groups might commandeer it.

Warning: Plot spoilers ahead.

The movie's title character carries out random acts of deadly violence, igniting a populist revolution. The story focuses on the pre-Joker Arthur Fleck, circa early 1980s Gotham — a sad-sack clown slowly unraveling under his troubles and finding solace in a gun and mask — and becoming a folk hero in the process.

It is improbably directed by Todd Phillips, the filmmaker behind the "Hangover" comedies, and stars Joaquin Phoenix. Adding to the mixed messages about the movie is that even some critics who have decried its emphasis on violence are lauding Phoenix's performance.

A lot on the line

The stakes are high for Warner Bros., whose DC Extended Universe has struggled to hit pay dirt at anywhere near the consistency of Disney's rival Marvel Cinematic Universe (with only one release, "Aquaman," of more than $1 billion in global box office to Marvel's nine).

That "Joker" won the Golden Lion at the Venice Film Festival — Warner Bros. is the first major Hollywood studio in the modern era to win the prize — ups the ante. The victory leapfrogs it ahead of Disney, which this year became the first studio to notch a best picture Oscar nomination for a comic book movie ("Black Panther").

But the talk at Toronto, which more than any other festival sets the tone for Hollywood's all-important upcoming Oscar season, shows that the stakes are a lot higher than just the battle for corporate bragging rights.

Some commentators have vigorously decried "Joker's" message. Time's Stephanie Zacharek wrote that the film "lionizes and glamorizes" Phoenix's character.

"In America, there's a mass shooting or attempted act of violence by a guy like Arthur practically every other week," she wrote. "And yet we're supposed to feel some sympathy for Arthur. There's a sick joke in there somewhere. Unfortunately, it's on us."

Those who disagree with her view have been confronting the essential questions surrounding the movie: By peering so closely at a killer, is Phillips more interested in understanding his mind than glorifying his thinking? Indict the mental health system that failed him, or cheer that he broke free from conventionality?

Let the arguing begin

At the post-screening gathering, a debate broke out among journalists and industry executives over whether the movie could become part of the texts cited by potential future mass shooters, and what that would mean. Even if the causation between media violence and the real-world shootings is statistically unproven, a few asked, couldn't the movie still become part of the problematic context for them?

Warner Bros. is understandably eager to play down any such talk, in part because rivals in similar situations have been forced to cancel movies. Most recently, Universal Pictures scrapped "The Hunt" after August's shootings in Ohio and Texas.

But it's also because the studio has been caught in this debate before. The studio's "The Dark Knight Rises" was playing at the theater in Aurora, Colo., in 2012 when a gunman opened fire on the audience, killing 12 people. The shooter cited the movie as an intentional choice for where he launched his attack.

Phillips maintains that his goal was not to make Fleck a hero. He has said that he has simply chosen to make a grittier movie about a villain than has been made before.

"How do you make a movie with white face and green hair and run it through as realistic [a] lens as possible?" Phillips said after the screening. "Because we don't believe you fall into a vat of acid and are turned that way," he said, referring to what the comic books say about how the Joker character was created.

From the moment the screening ended, the debate was on over whether Phillips had made a brilliantly inscrutable work or a movie as elastic as the protagonist's face. And while predictions vary widely on what sort of impact it will have, people seem to agree on one thing: "Joker" will have an impact.