End of Watch shows the post-Rodney King police department in Los Angeles

End of Watch gives viewers a glimpse of the new Los Angeles police department, now heavily Hispanic.

Michael Pena (left) and Jake Gyllenhaal play LAPD officers in this hard-hitting thriller.

He admits he knew nothing about how the Los Angeles Police Department actually worked, nor how they dealt with the gangs that control America's most notorious west coast locale. Yet Jake Gyllenhaal's innocence was soon shattered, on day one of researching his new movie, End of Watch.

"We were in fight training every morning," he says, of the five-month intensive course he and his co-star, Michael Pena, had to undergo prior to shooting the riveting, gritty police thriller, directed by David Ayer (of Training Day fame). "We were doing tactical training with live ammunition twice a week, ride-alongs two or three times a week [with the LAPD]. The first I went on, someone was murdered, in front of me."

Unlike his co-star and director - who both spent their formative years in the troubled neighbourhood - Gyllenhaal, a Columbia university graduate, had never set foot inside South Central LA, let alone come face to face with armed gangs peddling guns, drugs and, in some cases, women and children. His view of the police who do has now, not surprisingly, shifted.

"What we don't take into account is what it's like coming back from a night of work," the 31-year-old actor points out. "If you're working from 4pm to 4am and you get a call at 3am and have to deal with a shooting, or you're in a shootout, or you're dealing with a domestic violence case, or you're chasing a stolen car, or whatever, these things affect the officers. Then they come home, back into life. That's not talked about."

Gyllenhaal's co-star, Michael Pena - who's been a successful jobbing actor in Hollywood for nearly 20 years - believes it was Gyllenhaal who had the toughest role of all during the lightening-fast 22-day shoot. "It's not easy being the white dude," the 36-year-old says. "Seeing it through Jake's eyes, it reignited what I already knew. It sort of smacks you in the face."

End of Watch - which received a standing ovation following its world premiere at this year's Toronto International Film Festival - paints Gyllenhaal and Pena's characters to be as good as blood brothers. They attend each other's family gatherings, and spend every day in the patrol car together. They are inseparable. Much of the film is shot point of view as well (the LAPD carry cameras a lot of the time, like Gyllenhaal's Officer Taylor in the film). An even bigger twist, for some, is the fact that both police officers appear to be genuinely nice guys.

Director David Ayer explains. "Ironically, the way to do something fresh is to have them as good cops," he says. "The subject had kinda been done to death in a lot of ways, so we had to come up with something different. A friend of mine was in the LAPD for 14 years, eight of them he worked gangs, and a lot of these stories happened to him. So I just wanted to show how the real police in LA are. And shoot it in an interesting way."

The LAPD here is a far cry from the 1991 Rodney King-era force, which was still a largely white-controlled organisation. Now, it is heavily Hispanic. Even women make up a sizeable percentage. None of this, Ayer says, has really been told on screen. Until now. "They're just normal guys trying to live their lives, and that's what I wanted to show," he says of his two lead characters. "Behind the badge, this symbol of authority, it's the heart of a normal man wrestling with everyday issues - do I get married, do I have kids. I wanted to show the secret world of friendship within the secret world of the police, of two best friends talking."

The film is so focused Gyllenhaal and his partner, in fact, that their respective female co-stars, Anna Kendrick and America Ferrara, are almost left to just offer support when required. But its core values - of friendship, loyalty and commitment - are strong and grounded in both the men and women. It also carries with it a sense of realism previously glimpsed in Training Day, the Oscar-winning film David Ayer wrote over a decade ago.

"I got this one right," Ayer says (following a pair of false starts as a director, after the Denzel Washington thriller took off). "I finally made the movie I wanted to make, I finally found my voice as a director. Now I can hang up my team jersey and work in a different world."

Before he does so, Ayer is shooting another crime thriller - about the Drug Enforcement Agency (DEA) in Atlanta - which stars Arnold Schwarzenegger and Sam Worthington. A World War II film and a sci-fi actioner may follow.

As for Gyllenhaal, whose buzz cut in the film has now been replaced with a full head of hair and matching shaggy beard for a theatre run in New York, the experience has been overwhelming, to say the least.

"I have made some of the closest relationships I've had in my life so far [from this]," he says. "Three of the guys we worked with, they're some of my closest friends at this point. It has been such a huge, life-changing thing. It's just so different to anything I have ever done."

End of Watch screens Saturday 13th October at 6.15pm (Emirates Palace) and Sunday 14th October at 3.45pm (Vox 4).