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They have a sample of his DNA, a description from a survivor and a $500,000 reward, but detectives investigating the city's most notorious serial killer have hit a wall.

On Wednesday, they released a recording of a 1987 emergency call in hopes of tracking down the man dubbed the "Grim Sleeper," who has killed at least 11 times in nearly a quarter century.

"It's a long shot, that's for sure," said Detective Dennis Kilcoyne. "I am hoping a couple people call us. ... Maybe that will lead us to something."

Kilcoyne heads a squad of seven of the Los Angeles Police Department's top homicide detectives, who for nearly two years have been assigned exclusively to the case. The killer most recently struck Jan. 1, 2007, and his first known victim was in 1985.

Police have pored over investigative files from all the killings and are now focusing on the January 1987 slaying of Barbara Ware, a 23-year-old with a history of prostitution who was found shot to death in a South Los Angeles alley.

A man in the area saw a blue-and-white van dump her body. He called police with his account and gave the license plates from the van. Within about an hour, police had tracked the van to its registered address at a church.

"The engine was still warm to the touch," Kilcoyne said.

Several congregants were inside the now-defunct church but no one seemed to know anything.

"Then the trail stops there," said Kilcoyne. "It sounds like it was a pretty good road map for the investigation at the time and it just fizzled out."

Kilcoyne and his men hope to track down former churchgoers or even someone who knows the voice on the emergency call, made at a time before numbers were routinely traced.

Kilcoyne is accustomed to promising leads turning cold.

Six victims were found with the killer's DNA on them but a search of prisoner databases came up blank. Detectives went on to ask the California Department of Justice to run a DNA search that sought possible matches to the killer's relatives. It was the first time the controversial search was carried out in the U.S., Kilcoyne said.

"It didn't produce an answer," Kilcoyne said. "Nothing."

The suspect kills by gunshot or strangulation, in some cases both, usually after some kind of sexual contact. Ten victims were women, all were black and several were prostitutes. Kilcoyne said it's possible the male victim — Thomas Steele, shot to death in 1987 — was a friend of one of the victims or had discovered the killer's identity.

The bodies were all found outside, usually in the dirty alleyways tucked behind Western Avenue and Figueroa a few miles south of downtown.

The $500,000 award offer is thought to be the biggest ever in the city. Billboards announcing the offer loom over streets near where the victims were found.

"We still have no idea who this guy is," Kilcoyne said. "We've got a half-million-dollar reward out there on billboards and no one calls."

The killings were featured on the television show "America's Most Wanted" and dozens of tipsters called detectives after the case was first made public last year, but leads went nowhere.

The first round of killings happened at a time parts of the city were suffering from extreme violence and many young women fell prey to newfound addictions of crack cocaine and other drugs.

Kilcoyne said as many as 30 detectives investigated a series of deaths in the '80s but after several years passed and they exhausted all leads, they moved on.

"You can't have the resources tied up for that many years, just scratching your head," Kilcoyne said.

Police Chief William Bratton assembled Kilcoyne's squad in June 2007 after the death of the killer's most recent known victim, 25-year-old Janecia Peters, who was found shot to death in a trash bin in a graffiti-tagged alley off Western.

"We realized we've got a serious problem," Kilcoyne said. "This guy is still out there."

Because of the race of his victims, critics faulted the Police Department for not investigating the killings sooner and said the city was disinterested in the case.

Porter Alexander, 68, whose youngest daughter Monique Alexander was killed in 1988, said police initially seemed reluctant to investigate her death because there were signs she may have been involved in prostitution.

"They didn't show any strong concern," he said. "If I didn't call, I didn't get a call."

Police don't know why the killer took a 14-year hiatus but the gap led the LA Weekly newspaper, which first wrote about him, to dub him the "Grim Sleeper."

Investigators think the killer had other victims, but their bodies either were never found or investigators failed to connect him.

"You start putting bodies in commercial Dumpsters in the city," Kilcoyne said. "There's a lot of them in the landfill."

Kilcoyne thinks a woman found strangled in an alley in 1987 may turn out to be the killer's 12th victim.

One description of the suspect exists — from a woman who survived an attack in 1988. She recalled him driving an orange Pinto and offering her a ride to her sister's house.

After exchanging some lighthearted banter, she agreed to the driver's offer. He had chiseled features, a low afro and wore a black polo shirt. He would now be in his late 40s to early 60s.

Shortly after she got in the car, she said, he shot her. The woman said she didn't recognize the sound over the loud music he was playing, then she looked down.

"There was a gunshot wound in my chest," the woman said. He sexually assaulted her, pushed her from the car and left her for dead. The woman, whose number was provided by police, asked not to be named because she is the victim of a crime.

"I woke up in the dark, I was in the middle of the street," she said.

Jack Levin, professor of sociology and criminology at Northeastern University in Boston, said there are typically about 20 serial killers on the loose at any time in the U.S. and they average about 10 kills each. Other serial killers have claimed many more: Green River Killer Gary Ridgway pleaded guilty to killing 48 women in Washington.

Time could work in Kilcoyne's favor, as most serial killers are ultimately captured, Levin said.

"But there's a very good chance the police will have to wait for him to attack again," he said. "They have to wait until the killer makes the fatal mistake."