“Oh, my God—unbelievable, awful, amazing,” Dan Gilroy murmured, as he sifted through a box of Weegee photographs from the forties. Gilroy, a writer-director, was at the Steven Kasher Gallery, in Chelsea, last week, using its collection to explain how Weegee—connoisseur of the blood-spattered corpse—had inspired his new film, “Nightcrawler,” about a feral loner who roams Los Angeles, filming scenes of mayhem for the local news.

The fifty-five-year-old Gilroy, who wrote “The Bourne Legacy,” is as thin and pale as dental floss, with a sepulchral face and milky-blue eyes. He is the antithesis of beach volleyball. It all began, he said, when he came across Weegee’s book “Naked City,” in 1988: “I thought, What an amazing intersection of art and crime and commerce! But I couldn’t figure out how to plug into it. I wrote a treatment with a ‘Chinatown’ feel, only instead of being about water it was about a landfill.”

He shrugged in mild apology and continued: “Five years ago, I heard about these stringers-slash-nightcrawlers who drive around L.A. all night at a hundred miles an hour listening to ten police scanners—a modern update of Weegee. And I decided to set the film in that world and make it a character study.” His antihero, Lou (Jake Gyllenhaal), is a one-man startup who employs business bromides, then extortion and murder, to secure a monopoly on the most lurid images. “Ten years after the film ends, Lou would be running a major corporation, orchestrating a giant merger that puts fifty thousand people out of work,” Gilroy said. “But he’s not just a sociopath—he’s also very good at adapting.” He observed that Gyllenhaal played Lou as a human coyote who comes down from the hills at night to feed: “Jake lost twenty-eight pounds for the role, so he was literally starving on camera, desperate to consume.”

Gilroy held up “Arrest,” a 1940 shot of a wild-eyed woman resisting being frog-marched by a man in a trenchcoat. “I didn’t give Lou a backstory, and we don’t have the backstory here. I imagine that the woman’s son committed suicide. And that guy over there”—a dapper observer with a weedy pencil mustache—“seems intent, like he’s taking notes. He looks like a journalist.” He noted that the photographer was able to capture these hectic moments because “Weegee invented carrying a scanner”—his version was a shortwave radio—“and getting there ahead of the cops, then selling the images to the highest bidder.”

The director peered at Weegee’s circular stamp—“Credit Photo by Weegee the Famous”—and continued: “He used a Speed Graphic camera, had a ten-foot focus, and shot with flash to create what he called Rembrandt lighting. The flash isolates the drama—heightening the foreground against a black backdrop—and it distorts people, so they look like they’re playing a part onstage.” Lou rearranges accident scenes to make his money shots richer; Weegee, too, orchestrated shots, including his most famous image, “The Critic.” It shows Mrs. George Washington Kavanaugh and Lady Decies, imperious in white furs, arriving at the opening of the Metropolitan Opera—and being stared down by a haggard-looking woman Weegee had collected on the Bowery, got drunk, and brought uptown to incite the moment.

Gilroy examined “Dead on Arrival”: an extremely bloody hoodlum lies supine beside a car, an identifying tag looped around his left wrist. “It’s an incredibly brutal image—too violent for the Post today,” he said. “But there’s something beautiful about it, something tragic.” He was reminded that when he and Gyllenhaal toured L.A. with a nightcrawler named Howard Raishbrook they saw “a horrific car accident where three young girls had been ejected onto the street—bloody, awful, they were screaming in pain, we couldn’t look. But Howard, professionally, found an aesthetically pleasing angle from behind the fire truck—and then another stringer came running down and said, ‘You missed it,’ arguing that the really cool shot was from the overpass.”

Gilroy held up “Their First Murder,” a shot of an anguished woman (the victim’s aunt) surrounded by neighborhood children gleefully enjoying the tableau—which, unseen here, was actually the “Dead on Arrival” killing. “The smiling faces . . .” He shook his head. “It’s the same indictment I was going for in ‘Nightcrawler.’ The enjoyment of savagery is so deeply human. The worst dictators in history, after ordering the deaths of thousands, would smile and play with a puppy.”

“Nightcrawler,” Gilroy’s first turn as a director, is his big break. But as he prepared for its opening he resembled Weegee’s Bowery sot more than his uptown swells. Staring at the photographs, he said, “Later, Weegee went even further in distorting faces—he made even Marilyn Monroe seem incredibly ugly. I mean, look at us! We’re grotesque.” He pushed the box away—and then, a moment later, pulled it back.