The director revealed to Flicks and Bits that he greatly enjoyed watching old gangster movies to prepare for his latest project.
"There were a ton of movies that we looked at," Fleischer said. "I mean, some of the classic gangster movies from that era, like White Heat or Gun Crazy, they were ones we definitely looked at."
He further explained: "But there was also the tradition of gangster movies, whether it's something like Scarface, which wasn't set in the time, but it is a classic gangster movie - or even Goodfellas, it's a gangster movie, yet not a 1940s-era gangster movie.
"Then there's The Godfather, The Untouchables, LA Confidential, they were some classic movies we looked at. There were so many, it was great watching them again, 'researching'."
"It was tricky bringing that era to life, just because so little of it still exists, you know?" he said. "We had to find some buildings that are intact from that time period, and then also collect the cars and the clothes and the guns. Everything was period-accurate."
The director continued: "The attention to detail from our production designer Maher Ahmad was amazing - in terms of designing it and filling the sets, they felt really real and authentic. It was all real stuff from the period. All of that took a while to assemble, but it was worth it.
"And for me, I love when movies take you back in time so completely that you feel the texture and the richness of the places, but because we also wanted this film to feel contemporary, it called for a delicate balance."
Gangster Squad is now playing in the US and the UK. Watch a trailer below: