On the morning of Jan. 15, 1947, the body of a 22-year-old aspiring actress named Elizabeth Short was found naked, mutilated and cut in half in a vacant lot in the city of Los Angeles. Newspapers revealed the rest. Short was a small-town girl who, like so many others, worked odd jobs and oscillated between hotels and boarding houses, flirting with men at local bars in hopes of catching her big Hollywood break.

The papers dubbed her “Black Dahlia,” some said because she had flowers pinned in her dyed black hair. Her gruesome murder captivated the nation and consumed local headlines. The LAPD launched a theretofore unparalleled investigation into her murder, but despite dozens of confessions by both men and women, Short’s murder remains unsolved to this day.

Just 11 years later, a 10-year-old boy from LA named James Ellroy learned of his own mother’s murder; she had been strangled and dumped in an ivy patch near a local high school. The next year, the boy received Jack Webb’s book “The Badge” as a birthday gift, in which Webb discussed several LA crimes, among them the case of the Black Dahlia. The two women would be forever linked in Ellroy’s mind.

Ellroy grew up to be a crime novelist, but it wasn’t until 1987 that he dedicated his seventh book, “The Black Dahlia,” to exploring his obsession with the two murders. In the afterword to a new edition of the novel, timed to coincide with Brian De Palma’s film of the same name to be released on Sept. 15, he writes, “The initial fusing was sharply brief. The sustained process has been attenuated. It’s a torch song with no crescendo and diminishing chords.”

Ellroy’s book is a fictional account of the investigation into Short’s murder. The protagonist is Bucky Bleichert, a cop reluctantly assigned to the case who becomes progressively more obsessed with Short and with finding her killer. Ellroy was not granted access to the LAPD files; like many of his books, “The Black Dahlia” is an amalgam of fiction and nonfiction. On the surface, the novel is all about the famous 1947 murder, but it gets all of its turbulent energy from an undercurrent of unprocessed emotion stemming from Ellroy’s own tumultuous memories about his mother’s murder, memories he explored more thoroughly in his 1996 memoir, “My Dark Places.”

After that memoir, Ellroy seemed to put it all behind him. Having left LA in 1981, he was also ready to abandon his past. His last novel, “The Cold Six Thousand” published in 2001, was the second part of his Underworld U.S.A. trilogy about the United States in the 1960s. It had an abbreviated and staccato style. Publisher’s Weekly wrote that the novel “cuts like a dark 24-hour Beat poem and sounds like Jack Webb on crack.” It explored the mob, Las Vegas, the Klan, JFK’s assassination, the state of a nation. It spread itself away from the author’s insides, onto anyone and anything else that did not have to do with him, his personal loss or the sad, inexplicable murders of two lonely women in the city of LA.

But in 2004 Ellroy re-involved himself in the case by penning the foreword to “Black Dahlia Avenger,” a book written by veteran LAPD cop Steve Hodel, who claims his own father, physician George Hodel, killed Short. “I began the book unimpressed, and came away converted,” he wrote in support of Hodel’s theory.

Then a couple of months ago, Ellroy returned to LA for good, or so he declared in a trenchant essay for West magazine on July 30. And now he’s revisiting those old memories once again as he tours the country in promotion of the new edition of “The Black Dahlia” and De Palma’s movie, which stars Josh Hartnett, Hilary Swank and Scarlett Johansson.

“Here’s the thing,” he tells me when I call him on the phone. “This is my farewell tour to two things: my mother’s death and the Black Dahlia. It’s over. After this tour, I will never answer another question about these things. It’s an idea whose time has come and gone. … I have told the fucking story of my mother and the Black Dahlia 96 million fucking times.”

Ellroy sounds gruff, but he radiates tenderness, vulnerability and an old-fashioned heroism. “I’ve got no patience with men who mess with women or children or dogs,” he rasps. “I do feel closer to women than men. To this day — and I’m 58 years old, and I’ve been married twice, and I’ve had a lot of love affairs — I am always grateful when a woman is nice to me, and by that I mean less than brusque. I don’t take much for granted in this life.”

That platitude rings true coming from a man who spent his younger years engaged in petty theft, voyeurism and drug abuse, but who is today a successful novelist whose books are immediately optioned for films, especially after the success of the adaptation of his 1990 book “L.A. Confidential.”

“If you take money to write movies — and it’s a lot of money generally — you shouldn’t bite the hands that feed you, and say, ‘Oh well, I’m an artist, I’m better than they are.’ It’s ungrateful.

“But,” he adds semi-jokingly, “I can think it, and I often do.”

And though he was not consulted for the screenplay, he has only kind things to say about the upcoming movie, describing De Palma as “the ideal artist” to film his book. “It’s a very interesting adaptation of my book. It dramatically isolates many of my themes, impresses action, and there is a wrenching performance by Mia Kirshner as the doomed Elizabeth Short herself. And this was a decision that Brian De Palma and [screenwriter] Josh Friedman made, because it was my contention that she should not appear on screen in any kind of flashback or flash forward and that she should only be discussed and ruminated upon. But Mr. De Palma and Mr. Friedman decided that in order to humanize her and give some moral weight to her that she should appear.”

The endorsement is significant. Ellroy’s novel made him an unwitting authority on the Black Dahlia case; his support of Steve Hodel’s theory drew a wealth of attention to “Black Dahlia Avenger.” (Screen rights for that book have just been acquired by New Line Cinema.) Even so, Ellroy has attempted to distance himself from Hodel a bit, especially as Hodel’s claims have grown more untenable. “It’s the best theory yet, and I endorsed it in my introduction to Steve Hodel’s book, but it’s unprovable. Most of Steve Hodel’s assertions about the various other women that George Hodel killed are bullshit, and the idea that one of his minions killed my mother is insane. His ideas got more and more tenuous, and he started calling facts to conform to this one thesis.”

After he’s done hobnobbing with celebrities at film premieres in support of “Black Dahlia,” Ellroy intends to get back to work on the third part of the Underworld U.S.A. trilogy, which he says will cover America from the years 1968 to 1972. “We’ve got Nicaragua, gay Edgar Hoover, Howard Hughes, Vegas, mobsters, armored car heists, black militants, a lot of crazy shit.”

From then on, Ellroy has declared his intention to write only LA novels, to “reclaim” the city. “I want this place,” he asserts voraciously. “I want this place. I want to be here. I want to bay at the moon. … It’s ironic that I moved back to LA at this time. The movie will be released almost 25 years to the day that I left here. I had to come back. I got divorced. I met a woman up in San Francisco, she dumped my ass, and I decided I better get back here.”

Welcome back, Mr. Ellroy. I hope we’re ready.