Growing up just two miles from where EoW was shot, now called Newton, formerly known as South Central, Ayers is all about getting it right, the raw, grittiness of the underside of LA that's a far cry from the LA people think of, and while it would have been easier to shoot somewhere else as he puts it "the street signs would be wrong."
With the gritty cop genre dwindling, Ayer wanted to make sure he "nailed" this third film that he has both written and directed about the tough streets of his hometown.
"For Mr. Ayer the streets of Los Angeles are something of an addiction. He lived on them for a time, having been thrown out of the house by his parents, he said. Later he began to write his experiences into stories during service on an attack submarine in the Navy.
Back in Los Angeles by the 1990s, Mr. Ayer did some fix-up work on the home of a screenwriter, Wesley Strick, who encouraged him to write scripts — and he found his calling. Mr. Ayer was among the writers of “The Fast and the Furious,” and he wrote “Training Day.” Both were set here.
He then directed two Los Angeles cop films, “Harsh Times” (2005), with Christian Bale, and “Street Kings” (2008), with Keanu Reeves.
Neither was a hit. As Mr. Ayer looked for a next project, however, a friend advised him to stick with his roots and tell another cop story. “Explaining why I shouldn’t, I realized why I should,” Mr. Ayer said.
He put aside his fear of being type-cast as the go-to guy for the Los Angeles police genre to pursue what he now calls “the ultimate cop movie.” It aims to transcend clichés that have piled up over the years, he explained, by portraying a pair of local patrol officers, played by Mr. Gyllenhaal and Mr. Peña, who are not crazed or corrupt. Instead they bring fierce mutual loyalty and an unexpected sweetness to their pursuit of goodness in a bad world"
Ayer wanted to give the movie an new point of view and it becomes a key player in the movie. Jake shot much of the movie himself with the camera that was mounted on his his chest, capturing a true to life look at partners on the force. Of we know that the premise is that he is capturing this for a film class he is taking.
EoW was written in 6 days, late in 2010, and shot in just 22 in 2011. But it took 5 months of training," assisted by the Los Angeles County Sheriff’s Department, police departments in Los Angeles and Inglewood, and others", to make sure that Jake and Michael had it down to play part of the thin blue line.
The story was was partially based on stories told to Ayer "him by a police officer friend, who, among other things, described a pact under which patrol partners each promised to kill the other and care for his family if either were left hopelessly incapacitated." (could this be foreshadowing?)
Of course we know about the ride alongs, and we saw them with burned out cars, and on the shooting range. But the NY Times article fleshes it out a bit more:
"On the first of his many police ride-alongs, Mr. Gyllenhaal said in a telephone interview, the squad car arrived on the scene of a drug dealer’s murder. Later Mr. Gyllenhaal and Mr. Peña endured a controlled burn by fire officials in Orange County, in order to acquire what Mr. Ayer calls “muscle memory” that would help them to play a scene in a flaming house. 
In an unusual exercise with live ammunition, the actors learned to shoot past each other in what proved to be a lesson less in police tactics than in bonding.
“This guy has my life in his hands for real,” Mr. Gyllenhaal recalled thinking. “I realized, I finally knew what we were dealing with.” (Mr. Ayer said the actors were “safe all the time” during the exercise at a training ground in Burbank.)
Some scenes find Jake and Michael shooting the S%@% was shot, "in the style of a stage play, in a single day." And how does it start? Right on the streets of LA, in a chase, that required one of its producers, to run through some of the LA's toughest spot in search of places to shoot.
We will have to wait till September to see if Ayers gets it right.