CNN  — 

The “Joker” hit movie theaters this week despite a wave of criticism that it glorifies a killer and could encourage copycat attacks nationwide.

The movie featuring Joaquin Phoenix is about a marginalized clown that goes on a killing rampage. The story’s told in a manner that seeks to evoke empathy without rooting for him, says CNN’s Brian Lowry.

It takes place in 1981 and tells the backstory of Arthur Fleck, a failed stand-up comedian who finds salvation by turning to murder in Gotham City. Even before its release, Warner Bros. faced protests from the families of mass shooting victims who feared it would lead to violence or copycat attacks.

Heightened concern about the movie’s premiere grew because of the 2012 mass shooting at an Aurora, Colorado, movie theater on the opening night of “The Dark Knight Rises” – another Batman movie. That attack left 12 people dead and dozens wounded at a midnight showing.

Stepped up security nationwide

In a joint bulletin, the FBI and the Department of Homeland Security warned law enforcement after online threats called for mass shootings at movie showings. The bulletin shared with police this week said while federal authorities had no information leading to specific or credible threats to particular venues, they had received tips of threats posted on social media since at least May.

In response, major cities beefed up security for the movie’s opening night. The Los Angeles Police Department said it’d maintain a high presence at theaters and urged moviegoers to be vigilant and report anything unusual. Some