Jurors found a 63-year-old man guilty Thursday in the "Grim Sleeper" serial killings of nine women and a teenage girl over two decades in the South Los Angeles area.

Lonnie Franklin Jr., a former sanitation worker and mechanic for the Los Angeles Police Department, could face the death penalty when he is sentenced May 12. Franklin was found guilty on 10 first-degree murder counts and attempted murder, involving a woman who escaped, after a day of jury deliberations and two days of closing arguments earlier this week in Los Angeles Superior Court.

The verdicts came following months of testimony about the killings, which spanned from 1985 to 2007. They were dubbed the work of the "Grim Sleeper" after an apparent 14-year gap in the violence after 1988, when one victim survived a gunshot and escaped.

Much of the killing occurred during the crack cocaine epidemic and the killer preyed mostly on young black women, some of whom worked as prostitutes. Several other serial killers were active at the time in South Los Angeles and community members criticized police for not aggressively investigating the slayings because the victims were black and poor.

A task force was assigned to revisit the case after investigators failed to solves the crimes in the 1980s. Retired detective Dennis Kilcoyne was the head of the task force.

"It just dawned on me, it's been nine years since (the final victim) Janecia Peters was murdered," said Kilcoyne. "These families, it's not a club you want to belong to. I think the world of these families."

Kilcoyne retired three years ago, one year after Franklin's arrest.

A break came for investigators when DNA of Franklin's son, collected after a felony arrest, had similarities to genetic material left on the bodies of many of the victims.

An officer posing as a busboy later retrieved pizza crusts and napkins with Franklin's DNA while he was celebrating at a birthday party. It proved a match with material found on the breasts and clothing of many of the women and on the zip tie of a trash bag that held the curled-up body of the final victim, Janecia Peters. She was found Jan. 1, 2007, by someone who was rifling through a trash bin and noticed her red fingernails through a hole in the bag.

Jurors began deliberations Wednesday after a surprise from the defense. Defense lawyer Seymour Amster argued for the first time this week in the long-running trial that a "mystery man," an unnamed nephew of defendant Lonnie Franklin Jr., was the real killer.

"Each and every murder in this case could have been done by a mystery man with a mystery gun with mystery DNA," Amster said.

Deputy District Attorney Beth Silverman claimed that Amster had concocted an imaginary scenario at the last minute in the face of overwhelming evidence of guilt.

"The theory of the defense is basically the equivalent of the skies opening up, a space ship descending and murdering all these women," Silverman said as members in the audience snickered.

Police and prosecutors believe the killer had more victims and may not have paused during the apparent hiatus. Photos of nearly 200 women were discovered in Franklin's house after his arrest and some of the women in those photos have never been found.

Photos of Peters and Enietra Washington, the only known survivor, were among the trove of snapshots.

Washington's testimony provided the blueprint of how Franklin preyed on women, Silverman said. He lured her into his car, shot her in the chest, sexually assaulted her and then dumped her from the vehicle, Silverman said.

The bullet removed from Washington came from the same gun used to shoot or kill seven previous victims, most of whom had Franklin's DNA on them, Silverman said.

But Amster said that the case collapsed on Washington's testimony because of inconsistencies in her statements to police. Washington described an assailant who was younger than Franklin and pockmarked, Amster said.

Amster then introduced the new theme of the defense. He said the real killer had access to Franklin's Ford Pinto and had told Washington he was stopping at an "uncle's house" -- believed to be Franklin's -- to get money while she waited in the car.

"It was not Mr. Franklin," he said. "It was the nephew, this mystery man."

Silverman said Amster had distorted the evidence and that Washington's descriptions of Franklin were always consistent. Washington identified a photo of Franklin and she pointed him out in court. She said she was 100 percent sure he was the man who shot her and left her for dead.

Amster said prosecutors had built a circumstantial case using inferior science that found the DNA of unknown men on the victims. But Silverman said Amster had twisted the evidence so the expert testimony favored his case when it was convenient and that ballistics evidence or DNA connected Franklin to each victim.

"If there is some mystery man out there, how come we didn't pick up his DNA on victim after victim?" she said.