Wonder why “Gangster Squad” is opening in the dead zone of early January, despite boasting Sean Penn, Ryan Gosling and Emma Stone?

It was supposed to come out last September. But after a gunman killed 12 people in a Colorado theater in July, Warner Bros. had to reshoot a scene where gangsters fire into the audience through a movie theater screen.

Wonder whether it belongs in the slot, when Hollywood unloads junk that doesn’t deserve a prestigious release?

Well, yeah. It does.

It begins as energetic, clichéd nonsense and ends as irritating, clichéd nonsense. Director Ruben Fleischer and writer Will Beall set the tone at once: We’re in for a gratuitously violent ride in which mobsters and cops batter and blaze away at each other until all the dead guys lie in the dirt.

The title card “inspired by a true story,” unusually shameless when used before such a tissue of lies, suggests that a secret commando team of six officers approved by Police Chief Parker (Nick Nolte) was sent after gangster Mickey Cohen (Sean Penn).

The movie’s set in 1949, and the team consists of the artificially mixed bag of foot soldiers we used to see in World War II dramas. This group – yes, led by a guy called Sarge (Josh Brolin) – consists of a brainiac (Giovanni Ribisi), a laconic black guy (Anthony Mackie), a grizzled vet (Robert Patrick), a naïve Latino (Michael Peña) and a cynic (Ryan Gosling), who joins because he’s interested in Cohen’s moll (Emma Stone).

It’s obvious at once who will live and who won’t. We may be mildly distracted by crooks dying from electric drills to the head or savage, endless beatings – we’re supposed to enjoy those, when the ones being bludgeoned are gangsters – but we can see every moment coming, down to the disgusted, “High Noon” discarding of a badge.

Brolin keeps his dignity. Stone and Gosling, effective elsewhere, are lackadaisical. The raging Penn, on the other hand, froths at the mouth like a human cappuccino-maker.

At least he tries to inject life into the dialogue, which ranges from pseudo-hip remarks to plagiarism. Says Sarge, “Fighting the war taught me that the only thing necessary for the triumph of evil is for good men to do nothing.” That famous quote predates the movie by decades, and Beall swiped it, as he did every other element of the story.

I don’t expect movies to be historically accurate, but this one’s especially outrageous. Cohen was arrested for tax evasion, not murder; federal investigators gathered the evidence, not L.A. cops; and he died peacefully in his sleep at 62. But I guess we’re not going to get a movie titled “Fraud Squad” any time soon.