Director Shaul Schwarz tells the tales of music and cartels in “Narco Cultura.” (Cinedigm)

The second crime scene of the day caused Shaul Schwarz to tarry in Tijuana that afternoon four years ago. Some of the victims were still alive.

“That’s really rare,” he says during a recent visit to Washington. “Usually it’s all bodies.”

The freelance photographer had assigned himself to document the consequences of the drug war in northern Mexican cities. Living with so much death, he was becoming a connoisseur. His work appeared in major magazines. Yet he was still groping for the best way to convey the power the subject held for him.

After lingering longer than he intended that day, he jumped in his car and rushed two hours north to a club in Riverside, Calif., to see some bands that sang about the drug war. There was no time to change his clothes, and he walked in still smelling of death.

The group Buknas de Culiacan caught his attention. Their sound was a lilting, almost sweet sort of oompah music, driven by a tuba and an accordion, along with guitar, bass and drums. Band members brandished an imitation assault weapon on stage and had a bazooka in the van that would become their stage trademark. Their lyrics, in Spanish, were boastful odes to carrying an AK-47, killing rivals and making lots of money working for notorious narcotraffickers name-checked in the songs.

The sharply dressed audience sang along with gusto.

Fresh from the reality that inspired this fantasy, Schwarz was shocked. Then he was mesmerized.

“The scene was just so overwhelming, seeing these guys with the bazooka and everybody singing and all the people playing narco for a night,” he says. “That’s the day that I knew I was going to make a film.”

That film, opening Friday in Washington, is “Narco Cultura,” a documentary. The photojournalist, who had worked in video before, decided that a moving picture was the only way to capture the spellbound vertigo he experienced as he explored the frontier between crime and culture, murder and music.

There was a physical frontier as well, of course. Ciudad Juarez , separated from El Paso by a fence and a trickle of river, figures in the film more than Tijuana. Schwarz, 39, who was born in Israel and moved to New York in 1999, knows the psychic power of borders. He’s fascinated by how, for anyone with the right papers, a short stroll over a bridge connects two such vastly different worlds: In Juarez, in 2010, the film notes, 3,622 people were murdered. In El Paso, five.

Each contrasting reality has a protagonist in the film. Riccardo “Richi” Soto is a soft-spoken forensic crime scene investigator in his native Juarez.

“The only way I can help this city is through my work,” Soto says in the film, though he knows most murders won’t be solved.

Edgar Quintero, born and raised in Los Angeles, is the brash lead singer and songwriter for Buknas de Culiacan, an ascendant narcocorrido band. Corridos are a type of Mexican folk song featuring picaresque ballad-stories. Narcocorridos cast drug traffickers as outlaw heroes and macho Robin Hoods. The band’s name is derived from Buchanan’s Scotch, said to be favored by drug lords, according to Schwarz, and refers to the city Culiacan, near the Pacific Coast. Culiacan is the home base of the savage Sinaloa Cartel, whose takeover of the drug trade in Juarez was a cause of the killing in Soto’s city.

Schwarz and soundman Juan Bertran spent years following the characters, over multiple visits, building trust and gaining extraordinary access. To remain unobtrusive in potentially risky situations — the aftermath of shootouts, social gatherings in the presence of guns and drugs — they used a high-quality camera the size and shape of an ordinary still camera and either a portable microphone or a wireless mike on their protagonists.

Schwarz had served in the Israeli Air Force and as a photojournalist had covered conflict in Israeli-occupied territories, Kenya, Haiti and Afghanistan. The atmosphere of coiled menace in Juarez and Culiacan had a different quality to him.

“I saw more gunfights in a day in Gaza or in Afghanistan than I saw in those four years in Mexico,” he says. “But it’s so clear that it’s everywhere. You could kill on the bridge to the U.S. You could kill in the middle of the day. You could do whatever you want. You could bury 70 people in a grave in Durango that I visited that is smack in the middle of the city. How come nobody said anything?”

Knowing when to turn the camera off was a survival skill. It was safer not to probe any specific killing — a local crime reporter was gunned down early in the project, and four of Soto’s colleagues were assassinated — even though that went against the filmmakers’ journalistic instincts. But they weren’t making a movie about a single murder case.

“Our case is Juarez,” Schwarz says. “It’s an overall feeling. That’s why we came here, that’s why we’re taking the risk. We want to show the viewer how it feels to be in Juarez.”

Inspired by the shock of juxtaposition that he first felt at the club in Riverside, Schwarz alternates scenes of Soto at work and home in Juarez with scenes of Quintero trying to be the most successful narcocorrido recording artist he can be. The band tours from Atlanta to Seattle and fills a major theater in Los Angeles, singing lyrics such as:

I bring a bag full of ammo

Of pure AK-47 and .45 . . .

I am Sinaloan and very true

I have enemies, what can I do?

Yet Quintero has never set foot in Sinaloa. He decides he must make a pilgrimage to perform in Culiacan — “the motherland, where narco culture comes from,” the singer explains — and Schwarz tags along.

Here the story lines intersect, as Quintero glorifies the gang responsible for so many of the bullet-riddled corpses that Soto must recover.

Quintero is Schwarz’s bridge to his larger theme: how deeply the drug war has seeped into culture on both sides of the border. American drug consumers, gun merchants and music fans are all implicated. Outside Culiacan, a boy on a tractor wears a T-shirt depicting Buknas and Quintero. On YouTube, the band’s top videos attract 100,000 to 1 million viewers. High school girls in Tijuana say they’d like to be a narco’s girlfriend.

When investigators in Juarez hear a narcocorrido break into a police radio frequency, they know it signals another killing. Even when Soto tries to relax with his girlfriend at a party, the local band plays a narcocorrido — and Soto doesn’t seem surprised.

“If we want to change what tomorrow’s generation thinks, let’s talk about changing the reality,” Schwarz says, “because art is always going to mimic it.”

As Quintero says in the film, “If there wasn’t so much violence in Mexico, we wouldn’t have such badass corridos.”

“Narco Cultura” opens Friday at the West End Cinema, 2301 M Street NW, Washington, D.C. Rated R, in Spanish and English, with English subtitles.