The Trail of a Killer : Thirty-seven years after his mother’s murder, crime writer James Ellroy hopes to uncover the life of the woman and find out who took it away.

In his 1987 crime novel, “The Black Dahlia,” James Ellroy had the audacity--what he would call the “righteous au thorial authority”--to cook up a solution to Los Angeles’ most famous unsolved homicide.

Leading his readers on a tour of the City of Angels’ seediest streets, Ellroy wrote of a young homicide dick who became obsessed with the Dahlia--a would-be actress named Elizabeth Short who in 1947 was found slain and severed in two. In fiction, Ellroy did what no real detective has ever done: He made the Dahlia’s killer pay.

Now, Ellroy has set out to solve another decades-old Los Angeles-area killing. Fresh from a promotional tour for his acclaimed 11th novel, “American Tabloid” (Knopf, 1995), he has begun researching a book about the mysterious 1958 murder of Geneva Hilliker Ellroy, his own mother.

Crime literature may never be the same.

After all, this is the murder that Ellroy says made him the man he is today. The 47-year-old author traces his fascination with all things criminal back to the day his mother was found, strangled and half-nude, near Arroyo High School in El Monte. And he admits that over the years he has used her death to stir up interest in his novels.

“I’ve exploited it,” he says flatly, recalling how a previous publisher, eager to promote “The Black Dahlia,” encouraged him to tell interviewers about his past. “He said, ‘If you’re willing to talk about this on the media circuit, we can put you out there and sell some books.’ And he was right. I told the story 9 million times.”

A self-described “master self-promoter with a tight grip on a pop-psych show-and-tell,” Ellroy used to tell reporters that his mother--a divorced alcoholic who could sometimes be harsh to her son--got “whacked.” More than once, he referred to her slaying, which occurred when he was 10 years old, as “the Geneva snuff.”

But today his tone is fervent, not flip. Thirty-seven years since he lost her, he is trying to find his mother again, to recognize the woman who gave him voice.

“To one degree or another I’ve exploited her or ignored her. I’ve understood that for a long time. But now, I know the true force that this woman and her death has had on me,” he says, explaining that by investigating her murder, he hopes also to understand more about her life. “This is an attempt to go back, to portray the woman with love and, if possible, bring her killer to justice.”

*

So it is that Ellroy, whose raw, tautly written but very dark books have won him both a faithful following and a coterie of critics, has arrived in an uncharacteristically soft-spoken place. This is a man who made a career out of chronicling the lives of burned-out cops, has-been or never-was stool pigeons, two-bit snitches and three-time losers. This is a man who can--and does--use the words milieu and Zeitgeist in a single sentence, a 6-foot-3-inch espresso addict who manages to appear brooding even when wearing loud Reyn Spooner Hawaiian shirts (his favorite apparel).

This is no mama’s boy. On the contrary, Ellroy says he hated his mother when she died.

“On my 10th birthday in March, 1958, she said, ‘Now you’re a young man. You can decide if you want to live with your dad or live with me,’ ” he recalls. When he chose his father, “she whacked me in the face. I had made up my mind that was the last time she was going to do that and, of course, it was. . . . The next thing I know, she’s dead.”

Ellroy’s decision to reopen the investigation of his mother’s slaying came after a newspaper reporter-friend discovered Geneva Ellroy’s murder file while researching a story about unsolved San Gabriel Valley homicides. Ellroy had never thought to track down the file himself, but once he learned it was there, he couldn’t get it out of his head.

If nothing else, he knew, it would make a great story: a grown man confronting a gruesome incident from his childhood, a hardened crime novelist coming face to face with the most personal of crimes. He arranged to write a piece for GQ magazine about reading the murder file--a collection of police reports, mug shots and coroner’s data--for the first time. The article, called “My Mother’s Killer,” was a finalist for a National Magazine Award. But it didn’t give Ellroy the peace he’d hoped for.

“I thought the pictures would wound me,” he wrote in GQ. “I thought they would grant my old nightmare form. I thought I could touch the literal horror and somehow commute my life sentence. I was mistaken. The woman refused to grant me a reprieve.”

*

So, he resolved to go further, to expand the article into a book, to be titled “My Dark Places.”

Embarking on a real homicide investigation was a daunting task, even for someone who’d written about so many fictional ones. Ellroy hired a detective he’d met when he first viewed the murder file, Sgt. Bill Stoner, who was retiring after 32 years with the Los Angeles County Sheriff’s Department and was looking for a new challenge.

Stoner, a reserved man with a neat mustache and a modest manner, was the first to tell Ellroy that they were unlikely to solve the case. The killer’s trail was ice cold. So many years had elapsed that many of the key players--and perhaps the killer himself--were dead. Others would be hard-pressed to remember details of that hot June night in 1958 when Geneva Ellroy lost her life.

But this unusual partnership--Ellroy in his white Jack Purcell sneakers, Stoner in his wine-colored loafers--had one thing in its favor. Stoner knew from experience that on rare occasions the passing of years can unlock secrets: previously reluctant witnesses want to unburden their consciences before they die.

Today, Ellroy and Stoner have a particular person in mind who they hope will come forward, a woman they call simply the Blonde. It is only a matter of reaching her, they believe, to let her know they need her help.

*

Geneva Ellroy dressed pretty on the night she died. Her sleeveless blue and black dress was set off nicely by a blue-lined, full-length coat. She wore faux pearls--a simple necklace complemented by a huge ring on her left hand. It was a Saturday, her son was staying with his father, and she was going out.

She arrived at the Desert Inn, a bar on East Valley Boulevard in El Monte, about 8 o’clock. Several people remember that she was joined by a woman and a man. The man was 40ish, white, swarthy and about six feet tall. The woman was younger and described as “hard-faced.” She wore a brown summer dress and tied her blond hair back in a ponytail.

The Swarthy Man and Geneva Ellroy left the Desert Inn about 10 p.m. Twenty minutes later they pulled a dark green Oldsmobile into a nearby drive-in, Stan’s, and ordered a snack. The carhop remembers that they talked vivaciously and seemed to have been drinking. By 11 p.m., they were gone, but three hours later, they drove in again.

Geneva Ellroy ordered chili. She was chatting gaily, but her clothes looked disheveled, and the carhop speculated she and her companion had been necking. The Swarthy Man, meanwhile, looked sullen. He ordered coffee and acted bored with the woman at his side.

The couple left at 2:45 a.m. Eight hours later, Geneva Ellroy was found dead. One of her stockings was tied around her neck. Her broken necklace lay under her body, and 47 pearls were found scattered nearby.

When interviewed by police, patrons of the Desert Inn said that the Blonde and the Swarthy Man were not regulars. One hard-drinking customer said the Swarthy Man had given his name, but he couldn’t remember it. An artist made a sketch of the Swarthy Man, which was circulated to newspapers and law enforcement around Los Angeles County.

But police came up empty, lacking leads and suspects.

Today, the Desert Inn is a Mexican restaurant called Valenzuela’s. Stan’s Drive-In was demolished long ago. But the mystery remains, and Ellroy and Stoner say the Blonde is their best hope for solving it. They talk about her frequently, speculating about why she has remained silent.

“The Blonde is the key,” Stoner tells Ellroy. “Was she a girlfriend of your mother’s? Of the suspect’s? Maybe she’s married to the suspect.”

Ellroy picks up where Stoner leaves off. Maybe the Blonde was married to someone else who was criminally connected to the Swarthy Man. Maybe she feared reprisals. But surely, he says, surely she has told someone what she knows.

“She’s a barfly. A juicer,” says Ellroy. “These people shoot their mouths off.”

Stoner concurs. “She’s told somebody--maybe a bar acquaintance--about her girlfriend who was murdered, about how she was lucky it wasn’t her. All we have to do is hit the right person.”

If and when they do, they’ve made it easy for that person to get in touch. Ellroy has a toll-free tip line, which he repeats to anyone who will listen: (800) 717-6517.

*

Stoner and Ellroy have had some disappointments. One of the original investigating officers is dead and the other can’t remember much. They’ve found the carhop, whose memory is flawless, but she admitted she never was quite sure about the type of car the Swarthy Man drove.

They’ve talked to Geneva Ellroy’s landlady. She cried when she saw James, and provided him with some details about his mother he didn’t remember. She used to like to make popcorn, for example, and eat it with a spoon. But the landlady was no help when it came to identifying the Swarthy Man and the Blonde.

Ellroy and Stoner are working under a publisher’s deadline: The book must be written by mid-1996. If they don’t get their man by then, Ellroy will write about the search, about his fierce friendship with Stoner, about his mother’s life and his own. In some ways, he muses, such an outcome would be fittingly ironic.

“It [would be] Geneva Hilliker Ellroy’s last laugh,” he says, slipping briefly into her voice as he imagines what she’d say. “Jimmy, you exploited me and now . . . you’ve gotten three weeks on the New York Times bestseller list. You would have gotten 83 [weeks] if you’d found the killer before the hardcover was published!”

But Ellroy says his search will continue until the killer is caught. And if that day comes after deadline?

“Then [my publisher] is going to say, ‘Come here,’ ” Ellroy says, beckoning with a long finger. “ ‘Come here and write an addendum for the paperback edition.’ ”