Clarita Alia has visited the San Pedro public cemetery every week for the last two years, threading her way through the maze of concrete tombs.

When her 14-year-old son, Bobby Alia, was released from jail last year after being suspected of petty theft, she immediately took him to call on his brothers. From evening until dawn, they camped beside the graves of the two teenage boys, stabbed to death a year earlier in separate attacks. She warned Bobby to be on his guard or he might soon join them.

Two nights later, he did.

As Bobby got on a motorcycle after leaving a karaoke club, a short man in a black jacket and jeans buried a hunting knife in his back, Clarita recalled, citing witness accounts. Bobby got off the bike to flee but was stabbed again in the right shoulder. He scrambled for nearly a quarter-mile through the marketplace, clutching his shoulder to stanch the bleeding, before he stumbled over a chair and collapsed amid the food and coffee stalls.

Like his brothers, Bobby was swept up in a wave of unsolved killings in Davao. In the first nine months of this year there were 94 such killings, according to figures compiled by a coalition of human rights, legal and children's advocacy groups. Since 1999 there have been more than 200 and only one prosecution.

The murders have terrorized the poor here in the largest city in the southern Philippines. But local officials say they are untroubled by the killings, which they say have made Davao a safer city for tourists.

"I don't mind us being called the murder capital of the Philippines as long as those being killed are the bad guys," said Mayor Rodrigo R. Duterte, dubbed the "Dirty Harry of Davao" by the public. "From day one, I said henceforth Davao city will be very, very dangerous for criminals. I've been telling criminals it's a place where you can die any time. If that's a cue for anybody, that's fine."

Davao police attribute the murders to personal grudges between criminals and to gang violence. Many residents, however, say they think a death squad is operating with the blessing of local officials, targeting suspected drug peddlers, pickpockets and other petty thieves.

Duterte said in an interview that he did not know who was committing the murders, and he took responsibility for the lack of prosecutions. "I'm more interested in solving crimes against innocent people. I'm not at all interested in the killings of criminals, especially people involved with drugs," he said.

During his tenure, government officials said, the local crime rate has fallen, making Davao one of the safest major cities in the Philippines and winning it national plaudits. The city police department was honored last year by the national police commission as the country's top force. Duterte has been tapped by President Gloria Macapagal Arroyo as her special adviser on peace and order.

The vigilante killings are quietly cheered by local businessmen. "The criminals are being eliminated one by one," said Romeo J. Serra, president of the Davao City Chamber of Commerce and Industry.

Edmundo Acaylar, the city tourism officer, added that the murders have made this coastal city of 1.1 million a safer vacation destination. "I call it the process of expurgation. Whoever is doing it, I say very good and thank you," he said.

The dead are nearly all from the slums of Davao, a city where about a third of the families live below the official subsistence level. The young victims are often drawn from the growing ranks of street children, almost always dropouts who have left school to help their parents scrape out a living or to join gangs.

"This is a systematic, dramatic effort to eliminate the undesirables in society," said Bernie Mondragon, coordinator of the Kabataan Consortium of children's advocacy groups.

The killers frequently work in pairs, one acting as the assassin and the other as lookout, according to human rights groups and children's advocates. They sometimes dress in black, with caps partly hiding their faces, and often ride a motorcycle without a license plate.

"Now it seems that every crime deserves the death penalty. Even petty crimes are punishable by death, based on the justice system of these vigilantes," said Carlos T. Zarate, head of the Davao chapter of the Philippine bar association, which has condemned the killings.

"We believe the Davao death squad is financed and protected by forces that are coming from the state itself, either the local government or the local police," said Ariel Casilao, a leader of the Coalition Against Summary Executions. He added, "Whenever the mayor declares war on criminality, bodies are found on the street."

Clarita Alia, 48, a mother of seven whose skin has grown dark and tough from pushing a vegetable cart seven days a week in the city's main market, recalled that the police had come looking for her son Richard, 18, one night in July 2001. They accused him of robbery and assault but had no arrest warrant. "You can't take my son," she told them. The officers elbowed her aside, threatening her with arrest. But they did not take Richard. Clarita urged her son to leave town.

Two weeks later, as Richard was returning to the neighborhood, he stopped for a beer. When he stepped outside the cafe to urinate, two burly men jumped him, Clarita said, citing witness accounts. They punched him in the face and then stabbed him to death with a butcher's knife.

Christopher Alia, 16, died three months later. He had recently found work as a barker on a minibus after spending time in jail for sniffing glue.

During a lunch break, Christopher had paused at a roadside table for a plate of barbecue chicken. When he stood up to leave, an attacker described by witnesses as a tall man with a scarf wrapped around his face came at him with a butcher's knife.

Then there was Bobby. He had been jailed twice last year, once for carrying a knife and once on suspicion of stealing a cell phone. He was killed outside the karaoke club last November, moments after he had finished singing a number called "Paalam Na," or "Goodbye."

A brief police report confirms the basic details of the three murders. Chief Inspector Matthew Perlas Baccay, commander of the San Pedro precinct, said in an interview that the police investigation had stalled because of a lack of evidence, adding that the deaths likely resulted from a dispute between youth gangs. But social workers familiar with the Alia cases rejected this explanation.

Clarita is terrified that the violence is not over. Last month, she said, a stranger in a karaoke bar warned her that another son, Arnold, 25, would be next, ominously running an index finger across his throat as he said the name. Arnold has gone into hiding. The grandson constantly in Clarita's arms is Arnold's child.

A day after Clarita stoically recounted the saga of her sons in an interview, she took the baby on her weekly visit to the hilltop San Pedro cemetery. She made her way past the larger compounds of wrought iron and marble at the front, to the farthest, most crowded reaches on the back slope. There, where the grave sites are packed so tight that it's almost impossible navigate between them, she stepped nimbly from tomb to concrete tomb, grandchild in her arms, until she reached the resting place of her sons.

Their three tombs were stacked one atop another under a makeshift corrugated metal roof. The newest one, Bobby's, was still raw gray. Clarita had not been able to afford a proper white finish. A stone plaque bearing the names of Richard and Christopher lay loose on top. Bobby's name had not yet been added.

Clarita lit three long, yellow candles and placed them on the unfinished tomb. Then, finally, she wept.

"If my sons were guilty, they should have been charged in court. And if they were jailed, I would have accepted it because that would have been according to the law," she said, tears streaking her tough skin.

She tapped the tomb with her fingers, softly.

"I don't want my fourth child to die."