In Ruben Fleischer‘s new film, Josh Brolin heads a task force called the Gangster Squad. The Oscar-nominated actor plays a straight-laced detective named John O’Mara. The character and story are based on actual events that happened in 1940s Los Angeles. O’Mara and his team helped bring the notorious mobster Mickey Cohen to justice. A few weeks ago, Brolin participated in a press conference for Gangster Squad, where he dished on everything from shootouts to fighting Sean Penn.

What type of research did you do to get into the character of Sgt. John O’Mara?

Josh Brolin: We got to talk to some people. We got to talk to John O’Mara’s daughter. You create a composite character and see how it works. And then, you get to the set and Ryan [Gosling] is doing something this way and Sean [Penn] is doing something that way, and you gotta adjust and hopefully find the best dynamic that you can create on the set. It was the same thing with American Gangster… It was less of a laconic character when we filmed it, but in editing, we found it much better to have me shut up and go for more of that Bogey, Clint Eastwood type of thing. It seemed to balance things out better. Even what you do on the set isn’t necessarily right. Thank God for editing. But, this was more of a composite thing. You lend yourself to the romantic idea that you have of that time, and what that is for you personally.

How did you personally view O’Mara?

Josh Brolin: I think he has a lot of integrity. I like the fact that it’s this old idea of somebody who has the honor of not following the manual of what they said law was back then.  I think law was a lot less paranoid than it is now, and the boundaries of law were a lot more malleable then than they are now. Guys thought outside the box.  The good guy was not necessarily the good guy. He had to think dirty, in order to snuff out these guys who were trying to turn Los Angeles into the Wild West and into a cesspool. After he got back from WWII, I think he was shocked about how much Los Angeles had changed. And instead of being narcissistic and selfish, he thought about the future of his kids and all of the stuff that we think about now.  Whether we’re truly that kind of country or not, we were much more so, back then.

How did you guys get such a talented supporting cast?

Josh Brolin: You start these things out and you have this studio-propelled, value dream team, and you’re trying to get who’s of most value. It’s kind of great when that doesn’t necessarily work. You go down this idea of rung on the ladder, and they turn out to be the best actors you could possibly get for those parts. I think we came out with an amazing cast that wouldn’t necessarily do smaller parts like this ’cause a lot of those guys are lead guys now.  It was great because I’m usually the guy who’s fucking around all the time on the set. With this one, I got to stand back. When you have Anthony Mackie and Michael Peña and Robert Patrick on a set together, it’s absolute fucking chaos. It’s a lot of fun to be able to watch. So, they created a vortex that became what you see on film, which I think is the great exhale of this film. Within all this testosterone, it’s because of them that you get to take a breath. And then, the impact of all the other stuff is much more apparent because of that.

How was it working opposite Sean Penn?

Josh Brolin: Sean is great. We’ve known each other for a long time. I don’t find him very intense, myself. He’s an amazing actor. We have a lot of fun. We work similarly, and we have a lot of fun on the set. We don’t go around with furrowed brows. We have a place to springboard from and dive into, so working with him is a great pleasure. When you’re looking at somebody in the pupil, and they’re doing their best to be as intense as they can and you’re doing the same, and you know each other as well as we do, it’s kind of dumb. But, hopefully audiences will enjoy it.

So it was pretty easy for you?

Josh Brolin: The great thing about him is that you look at him and go, ‘That’s the guy who was Harvey Milk.’  That’s the shocking thing about Sean. His conviction is so complete when he’s doing something, but then you remember, as a fan, ‘Holy shit, this is the same guy who did this. This is the guy who has the ability to be as vulnerable as he is intense.’ That’s what makes him so special, at least to me.

What was the most difficult scene to shoot?

Josh Brolin: I think the fight with Sean [Penn] was the most difficult. Sean didn’t rehearse as much as I did, so his fists were flying wildly during the fight, hoping they got something usable. It was a tough fight that we rehearsed for many, many, many weeks and I love the way that it turned out. But I think both of us, being the current and ex-smokers that we are, it’s the most challenging, on an oxygen level.

Did any punches connect?

Josh Brolin: Possibly.

What was it like to shoot that big gunfight at the Plaza Hotel?

Josh Brolin: Those things are so serious, and you have to make decisions. It’s all so super cool, but the reality is that you’re just an actor, living this childlike existence. It’s kind of fun, but at the same time it’s very serious. We’ve had a lot of things come up lately that make it very serious. The impact that that has, you have to understand that, when you’re doing something like that, you’re lending to the story that you’ve already decided to do. It’s not about, ‘How do we treat this in a way that might be more respectful than not?’ You’ve already decided to do that type of film. It was a lot of fun doing it, but for a guy who doesn’t have any guns myself, I was a little nervous. I live in a very Republican area in Central Coast, California surrounded by gun-toting guys. I like tactile things. I miss a good fight. The gun thing, I’ll show you the gag reel,  and that will show you how lost we were.

Is there a special sensitivity about this kind of gun violence, due to recent events?

Josh Brolin: Of course, there’s a sensitivity. But, you have to look at the grand scheme of things from a universal standpoint. You have video games. You have psycho-pharmaceuticals. You have the lowest employment. You have parents who aren’t home. You have CNN, who gloms onto the worst of what’s going on, and not necessarily the best or the most heroic. There are many different factors. There’s no one reason. There’s always been violence in movies, and there will always be violence in movies. Whether it lends to the one psychotic that’s out there, thinking the worst thoughts you could possibly thing, is always going to be a mystery.

What point do you want to drive home with this film?

Josh Brolin: There’s no reason why L.A. shouldn’t have become Chicago and New York. There’s absolutely no reason other than you can’t walk everywhere.

Gangster Squad is playing in theaters now.