A part of the film had to be redone because the scene mirrored the Colorado shootings last July, where 12 people were killed and 59 injured as they watched a midnight screening of Christopher Nolan's The Dark Night Rises.
The Canadian actor, who plays LAPD detective Jerry Wooters in the crime thriller, said: "The thing is it's a testament to the kind of person that Ruben is because it was the highlight of the film.
"It was definitely the most memorable thing in the film and so for him to immediately cut it, I was so impressed."
The Zombieland filmmaker admitted he is proud that he changed the scene, despite the four-month delay.
"It was the respectful thing to do to delay the release," he said.
"I don't think it would have been appropriate to release the film with the theatre sequence in it so I'm proud of the fact that we decided to change it."
After the shootings, Warner Bros immediately pulled Gangster Squad trailers from cinemas and asked Ruben to re-shoot parts of the film, which is in cinemas now.
"We replaced the Grauman Chinese Theatre sequence with the Chinatown sequence," explained the 38-year-old director.