By Chris Summers BBC News

The Black Dahlia, starring Scarlett Johansson and Josh Hartnett, has had its world premiere at the Venice Film Festival. The film, based on a horrific murder 60 years ago, will be out in cinemas in the UK and US next month, but what is it about the case which continues to fascinate writers and film-makers?

Why Black Dahlia? The name is believed to be a corruption of Blue Dahlia, a 1946 film noir written by Raymond Chandler and starring Alan Ladd and Veronica Lake Elizabeth Short was christened the Black Dahlia by Los Angeles journalists, who later came up with the Red Chrysanthemum and Blue Orchid cases Black Dahlia was a reference to Miss Short's black hair or her habit of dressing in black

It began when the hideously mutilated body of a young woman was discovered on wasteland in Los Angeles one morning in January 1947.

She had been cut in half and her face slashed.

Police identified her as an aspiring actress, 22-year-old Elizabeth Short, known to friends as Beth or Betty.

Because of her raven hair and her preference for dark clothes, she was dubbed by one reporter as the Black Dahlia and the name stuck.

Several factors combined to make the story gold dust for the 1940s Los Angeles press - the victim was beautiful (and white), was on the fringes of Hollywood and had been mutilated in the most unspeakable fashion.

The story made front-page news, not just in Los Angeles but across the United States, and the papers followed every twist and turn of the investigation.

But, despite numerous suspects being arrested, no-one was ever charged and the case is still unsolved.

Scarlett Johansson is made for film noir

Forty years later, just when the story was beginning to fade from the collective memory, James Ellroy produced the eponymous novel, a fictionalised retelling of the case from the point of view of two detectives - the muscular and hard-drinking Lee Blanchard and the steadier, more ambitious Bucky Bleichert.

Well cast

The book, with its fantastically realistic yet politically incorrect dialogue, became an instant classic and now two decades on it has been turned into a movie by Universal Pictures, with Canadian actress Mia Kirshner as the Dahlia.

Scarlett Johansson, who plays Blanchard's girlfriend, seems almost perfectly cast for a role in the Black Dahlia.

Her classic features, smoky, breathless voice and knowing looks seem tailor-made for the cinema noir of 1940s Los Angeles. She might almost have stepped off one of Ellroy's pages.

But what is it about the Black Dahlia case that continues to intrigue writers and artists?

Betty always dressed in black as a gimmick to impress casting directors when she made rounds with the other girls The Black Dahlia, by James Ellroy

Ellroy says: "The Black Dahlia case continues to be the greatest single unsolved murder in American history."

American journalist and author Julia Scheeres said the case had all the elements which added up to make it a great tale.

"A beautiful young woman who wanted to be a Hollywood star, cut in half and dumped naked in a field. It became part of our cultural memory," she said.

She told the BBC News website: "The thing that haunts people is that the murderer has never been caught. He may now be a very old man, he may have moved out of the state, or abroad, or he may be dead. Who knows what he went on and did."

Who was the killer?

Ms Scheeres said: "There have been a glut of books about the case and some of the theories about who the killer was are preposterous. One of them suggested it was Orson Welles, because he had a magic act involving sawing a woman in half."

The last person to see her alive was 25-year-old salesman Robert "Red" Manley, who picked her up in San Diego and took her to a motel.

The thing that haunts people is that the murderer has never been caught...Who knows what he went on and did Julia Scheeres Author

The next day he took her to Los Angeles and dropped her in the lobby of the Biltmore Hotel.

Manley was interrogated for hours by detectives and later passed a lie detector test. In 1954 he was injected with sodium pentothal, the so-called truth drug, by detectives and was again cleared of any involvement. He died in 1986.

Over the years hundreds of people have come forward claiming to either be the killer or to know who he was, but those who were not cranks just turned out to be well-meaning but mistaken.

So the killer of the Black Dahlia has, as they say in LA, "beaten the rap".

But then the legend is all the better for being unsolved - just look at how many books and films Jack The Ripper has spawned.

The Black Dahlia opens in both the UK and the US on 15 September.