Since then, Ayer has moved up to directing gritty films centered around the Los Angeles Police Department, including "Harsh Times" starring Christian Bale and "Street Kings" with Keanu Reeves.

On Friday, Ayer's latest movie, "End of Watch," which he also wrote, opens in U.S. theaters. It portrays Los Angeles police officers in a more noble light, and stars Jake Gyllenhaal and Michael Pena as dedicated cops who are depicted going about their daily lives at work and at home.

Ayer talked with Reuters about his new movie, how it differs from his previous films and why he is secretly jealous of police officers.

Q: What made you decide to forgo police corruption and show the good guys on the force?

A: "Unfortunately for most people, when law enforcement enters our lives it's in a negative context - traffic tickets, or something bad has happened and we need help. We tend to only see cops at the worst times and never in the best of times. I have a lot of friends who are cops and I wanted to (show the positive side). This film is about two best friends and it shows what it's like to work the streets in a way few films have done before."

Q: Apparently you're a bottomless pit for cop stories. Where did the inspiration come from for this particular angle?

A: "I've always been struck by how cops would see heinous events on the streets and then have to go home and be a dad, a husband, and not bring the streets home. I was amazed by their ability to do that and thought there was great nobility in that."

Q: Unsympathetic cops like Denzel Washington in "Training Day" or Kurt Russell in your 2002 adaptation of James Ellroy's "Dark Blue" were exciting to watch on screen because of their antics. How do you make good guys exciting?

A: "You focus on character. The whole movie lives or dies on the relationship between Jake and Mike's characters. That's where I put all the primary work - getting the actors to become best friends, to play that chemistry, to play that history, so they could take us so deep inside their relationship that we hang on their every word."

Q: What kind of training did the actors go through to be as authentic as possible?

A: "These guys did five months of ride-alongs, tactical training, firearms training, vehicle training. The actual shoot was almost a relief because they finally got to apply what they learned."

Q: The film is shot in a documentary style, with various points of view from different video cameras, dashboard cams and cell phones that are used by the film's cops and gang members. Was that challenging to shoot?

A: "One of the biggest challenges was designing a camera to capture some of the images because the traditional cameras (that the average individual would use in real life) weren't of a resolution for theatrical release. So I had to work with a vendor to get cameras redesigned and miniaturized that we could actually mount on the actors."

Q: Did that affect performances?

A: "On a traditional set, the equipment set up will tell you exactly what is being photographed and then the actors will play to the camera. On this set, nobody ever knew when they were on camera. There was no way an actor could predict that this was their close-up. So that helped create these amazing, natural performances."

Q: Knowing cops and writing about them over the years, do you have any interest in actually being one?

A: "I probably know more about law enforcement than I'll ever need, but I'll stick to writing. I'll be honest, seeing these cops together, seeing how they interact, seeing this sort of community and how cool they are with each other, it really made me jealous. It was like, 'Wow, I would love to be a part of something like that.'"

Q: What are your hopes for this film?

A: "You know how people who see our service men and women in uniform, go up and shake their hands, and thank them for their service? I hope somebody does that to a cop."

Q: Your next film, "Ten," stars Arnold Schwarzenegger and Sam Worthington. Is this another cop movie?

A: "It's the DEA (Drug Enforcement Administration). We're kicking it up to the national level!"

(Editing by Jill Serjeant and Matthew Lewis)

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