No one here could ever figure out what brought Paula Vance from her last known address in Alexandria's Arlandria neighborhood to the alley behind the vacant athletic club where they found her body.

Hers had been a life lived on the streets and in the shadows, according to investigators, who found no friends or family to vouch for her existence, just a short, sad record of arrests for prostitution and petty crime. Even her February 1998 death -- a brutal rape and strangulation caught on grainy surveillance videotape -- made barely a ripple in a city already wracked by years of daily unrelenting violence.

Until now.

A homicide detective haunted by the slaying followed a trail of DNA evidence that led not only to a suspect but also to at least 11 other previously unlinked slayings over the course of a decade in impoverished south Los Angeles -- and multiple charges against a man who police now say was the most prolific serial killer in the city's history.

But while the new case against former pizza deliveryman and convicted rapist Chester D. Turner, 37, is being lauded as an exemplar of intrepid detective work, it has also raised troubling issues for Los Angeles. A mentally retarded janitor spent nine years in prison for three murders that have now been linked to Turner. Attorneys for the man, who has since been released, have filed suit, claiming investigators coerced a false confession and overlooked evidence that could have exonerated him.

And in a city that once made morbid icons of such mass murderers as the Hillside Strangler and the Manson "family," it now seems that the violent deaths of a dozen or so women in one hardscrabble neighborhood went virtually unnoticed and unmourned.

"There are no marches, no candlelight vigils," said Kerman Maddox, a politically active businessman and college instructor in south Los Angeles. "No one's saying, 'Let's get to the bottom of this.' They're numb to it."

The numbness set in during a period of unprecedented violence in the city, starting with the crack epidemic of the late 1980s, growing with a rise in gang activity and climaxing around the time of the Rodney King riots in 1992 -- a year when a record 1,095 homicides were reported in L.A.

In such an atmosphere, Turner's alleged killing spree -- from 1987 to 1998 -- barely stood out. And such violence was just part of the scenery in the crime-scarred neighborhood known as the Figueroa Street corridor, a 30-block stretch of vagrant motels and boarded-up storefronts where Turner spent much of his life and where all but two of the victims were found.

Most of the victims were homeless women, prostitutes or drug addicts -- women who in life had drawn little regard from their neighbors and whose deaths generated little outrage. Turner, meanwhile, did little to draw attention to himself during those years. Police say the burly high school dropout and sometime maintenance man had amassed an unspectacular criminal record of car theft and drug violations -- and nothing to mark him as a violent sexual predator.

Certainly, Turner's name never came to the attention of Detective Cliff Shepard -- not during his years as a patrol officer in south Los Angeles in the 1980s, nor when he was investigating Vance's death with the homicide squad in 1998.

Vance had been found north of the Figueroa neighborhood in a part of the city's downtown that is generally deserted at night. Her last minutes were partially captured by several security cameras that never gave a clear picture of her killer's face but left Shepard chilled.

"It frustrated us," he said. After police saw the video, "it was our belief this wasn't his first time, and it wasn't his last." The killer seemed to have a plan, he said. The video showed the man and Vance casually talking for several minutes before he suddenly attacked her -- then calmly walked away 20 minutes later.

Shepard continued to chip away at the case when he was transferred to a newly formed cold-case squad in 2001. For several months, he and his colleagues rushed to submit genetic evidence to California's DNA database of convicted felons, from as many unsolved cases as they could, during a brief period when the state was paying to process the city's queries.

Last year, they finally got a hit. In September, Shepard was notified that bodily fluids found on Vance's corpse had a genetic signature matching that of Turner -- who, a year earlier, had been convicted of sexually assaulting a 47-year-old woman and sentenced to eight years in prison.

But that wasn't all. On the same day, Shepard's partner, Detective Jose Ramirez, was notified that the database had produced a match to evidence he had submitted from the unsolved 1996 strangulation death of 45-year-old Mildred Beasley, a Carson, Calif., woman who vanished while visiting friends in south Los Angeles.

It was also Turner.

The revelation prompted the detectives to scour the files for other unsolved killings of similar circumstances and analyze any surviving DNA evidence. More hits kept coming in.

"After we got five we thought, when is this going to end?" Shepard recalled. "We knew he must be good for more."

The files led them to cases marked solved as well as unsolved, including three 1992 murders for which a mentally disabled man named David Allen Jones, now 45 years old, had been sentenced to life in prison.

Shepard said he began exploring the Jones case in part to see if some of the unsolved murders could be linked to Jones. Instead, DNA tests -- which had never been performed leading up to Jones's 1995 trial -- did not tie him to any unsolved murders. In fact, the DNA tests exonerated Jones in two of the cases he was convicted of and implicated Turner. In the third case, police say other evidence may link Turner to the killing. In March, the Los Angeles County district attorney's office quietly arranged for Jones's release while the investigation into Turner continued.

Prosecutors have now charged Turner with 10 murders -- his attorneys say he will plead not guilty -- but not with any of the three cases for which Jones was convicted. Prosecutors say more charges could follow; for now, though, those cases are the subject of a lawsuit by Jones's attorney, who complains that police overlooked the fact that all three victims were found with the somewhat rare blood type A -- Turner's type -- on their bodies, and no evidence of Jones's type O.

Lawyer Gigi Gordon maintains that the confession that helped convict Jones, who has an IQ of 62, was coerced.

"I've never seen a mentally retarded serial killer," she said. "They don't kill four people and not leave a trace, and you can get such a person to say anything."

Meanwhile, Johnna Edwards, whose mother's death in 1992 was originally pinned to Jones, expressed horror and anger over the times she remembers seeing Turner walk around her neighborhood in subsequent years. "Not only did you wrongfully convict this man, you left me and my sisters exposed to this," she said.

For Shepard, though, it's another thought that haunts: the half a dozen or so Figueroa area cold cases that did not yield evidence of Turner.

"We still have murders out there of women who were killed by similar murderers, and Chester Turner didn't do those," Shepard said. "We still have other murderers out there."

DNA evidence links Chester D. Turner, a convicted rapist, to the slayings of 12 women. Victims' family members look on, behind a poster of Turner and the victims, as police announce the findings. George Williams and Jerri Johnson, mother of victim Andrea Triplett, react.