“I see a multicultural hellhole. Overpopulated, egregiously smoggy. I've moved back here after 25 years away. I'm thrilled to be here.” James Ellroy, Los Angeles' most outspoken prodigal son, has returned home.

The author of L.A. opuses such as L.A. Confidential , The Big Nowhere and The Black Dahlia , Ellroy's obsession with the City of Angels and hard-boiled frankness belongs to a different time when private eyes, pimps, Hollywood moguls and aspiring actresses ran a city with infinite promise and infinite tragedy in the post-war boom.

“In 1986, my novel The Black Dahlia was optioned,” Ellroy says. “I'm a realist. I grew up on the edge of Hollywood – my old man was Rita Hayworth's business manager in the late '40s and allegedly poured her the pork on several notable occasions. So I know that the motion picture option is to the finished and released movie what the first kiss is to the fiftieth monogamous heterosexual anniversary. I never thought it would be a movie let alone a good movie. I have been very surprised.”

Ellroy is a man of immersion. He is unconcerned with the L.A.-now. He doesn't own a television or a computer, writes entirely by hand and spends much of his time living the L.A.-then, in a city where his mother and an aspiring actress named Elizabeth Short were murdered nine years apart, their killers never caught, their bodies splayed out on the pages of history.

“I isolate myself from popular culture. I bury my head in the sand and limit my intellectual intake to the period of time I'm writing about,” Ellroy says. “I lie in bed. I lie upon a couch and brood. And think.”

Director Brian de Palma ( Scarface , The Untouchables ) helms Ellroy's ambitious, fictionalized dramatization of the events surrounding one of Hollywood's most infamous murders. On Jan. 15, 1947, Elizabeth Short's eviscerated, mutilated body was found near Leimert Park in downtown L.A. While the girl's youthful beauty and raven hair earned her the nickname The Black Dahlia in the frenzy of newspaper coverage around town, her killer was never found.

In Ellroy's novel and de Palma's film, the detective duo of Lee Blanchard (Aaron Eckhart) and Bucky Bleichert (Josh Hartnett) pursue the case with single-minded determination to uncover the truth, from shootouts with gangsters to the palatial estate of the aristocratic Linscott family and their mysterious daughter Madeleine (Hilary Swank).

Cutting between Blanchard and Bleichert is the glamorous Kay Lake (Scarlett Johansson), a love interest for both men. In characteristic film noir fashion, no one is exactly who they seem to be and nothing is certain until the smoke from the last gunshot clears.

Ellroy has said that he sees some of himself in Hartnett's character of Bleichert, with his own investigation of his mother's death paralleling that of the police investigation of the Dahlia case.

“It was kind of obvious he'd written from a personal perspective,” Hartnett says, “because it's a first person narrative and because he's said many times that this book was written in this sort of way that exorcised the demons that were haunting him due to his mother's death. The Dahlia and his mother's murder were inextricably linked for him. And so I assume that there was some sort of autobiographical tendencies to the character.”

Johansson also considered her own links to the past, and says she empathizes with Elizabeth Short's struggles to find fame and success in Hollywood.

“I have a lot of friends who are very talented actors and musicians who struggle. You've got a one-in-a-million chance here, and all you have to do is come to L.A. and everybody's trying to get involved in the industry somehow,” she says.

L.A.-then becomes L.A.-now. In this town, the angels of our better nature do not always win out. Johansson continues.

“Anytime that you are involved in a field that's revolving around vanity of some sort with a high rate of failure, you have a breed of desperation that doesn't always have a happy ending.”

The Black Dahlia releases in theaters Sept. 15.