By the time the mob was finished with Tyrone Clarke, all that was left of the 16-year-old was what his own mother later described to reporters as "just a bloody pulp."

About 30 boys and young men had chased him down, beating him with cricket bats and metal scaffolding poles before he was stabbed three times in the heart on April 22, 2004, in a tough neighborhood of south Leeds known as Beeston.

Four youths were convicted of Clarke's murder this year, drawing prison sentences ranging from nine to 12 years. That Clarke was black and the mob was Pakistani did not, the presiding judge ruled, make it a racial killing. More complex factors including drugs and gang rivalries were at play, investigators decided.

Today, with police cordoning off the downtrodden blocks where three young suspects in London's suicide bombings lived, people here are searching for answers to the same troubling question: What feeds the murderous rage that ticks quietly in some hearts here?

A multiethnic enclave in one of England's largest cities, Beeston has long had racial tension on a slow boil, but police and community activists now fear that the resentment and wariness common among the immigrant generation can harden into hatred and violence in their British-born children.

At the Leeds Racial Harassment Project, director Shakeel Meer said: "They've developed their own very different culture within Islam, and they're not totally Pakistani or totally Islamic, and they're not totally British, either. These kids face quite an identity crisis. They're fighting to assert themselves not on one or two fronts, but in three or four different directions."

In the aftermath of the bloodshed to the south in London, authorities, religious leaders and community activists are trying to keep racial tensions in Leeds at bay. But the candlelight peace vigils are scoffed at by the white teenagers who complain about Pakistanis playing soccer in "our park," and the multicultural solidarity picnics are of little help to the pub-keeper whose parking lot one recent evening suddenly teemed with Asian gang members seeking to back up a member involved in a drunken brawl.

In Beeston now, there is a familiar drill on the streets of tight rowhouses in rubbled lanes: Police raid a new address suspected of having something to do with the London bombs. Residents are bustled away to be questioned or arrested. Neighbors peer out grimy windows or step into the back alley to watch.

Then comes the truck with metal poles clattering in the back, and workers in yellow hard hats who drill into the scabbed brick. Soon the house is encased in scaffolding three stories high. Then it's wrapped with thick sheets of plastic until the whole place resembles a gargantuan shower stall.

As the forensic teams, tucked out of sight, continue their searches for evidence in the London bombings, the troubled neighborhood is left to carry on a search of its own, behind facades equally opaque.

With a population of 715,000, Leeds is 91 percent white but home to 75 nationalities. Its history of immigration dates to the Irish Catholic builders who came in search of work in the late 1800s. Today, South Asians and their British-born offspring form the largest minority group -- 4.5 percent -- and mosques spring up alongside the spires and stained glass of Anglican churches.

Government statistics also show that the 10 percent unemployment rate among minorities in Leeds is double that of whites, and in a neighborhood like Beeston, social workers say, the competition for limited resources has bred a desperate and potentially dangerous new underclass.

In Beeston, teenage Irish mothers trundled babies across the broken sidewalks this week without greeting the veiled Muslim women chatting in neighborly clusters over low garden walls. In the park where Tyrone Clarke died, blacks cheered on one another in patois as they played ball by themselves while Pakistanis did the same nearby.

Five white teenagers smoking marijuana watched with a contempt they didn't bother to disguise.

"They start fights with us because we're white," said Damien Woodham, 18. "They're [expletive] racist."

His friend Martin Davison, also 18, complained that the park "used to be ours, but now," he said, using a racial slur, "they don't let the white lads cross."

For 12 years, Lani Ralph has been an outreach counselor in the nearby city of Bradford, where tensions along similar ethnic lines erupted in race riots a few years ago. The frustration and rage among young people has become so high that she now specializes in anger management for 13- to 17-year-olds. It won't be long, she suspects, before Leeds will follow suit.

"The Asian kids here are very well community-minded, they get together, back each other up," Ralph said. But that loyalty also has created loose-knit gangs, mustered as needed by mobile-phone messages.

"It makes them powerful," Ralph said. "They can control something: the streets."

The harder-core element falls into drug dealing and pimping, she added. "They've lost their way here. . . . It is so sad. I don't know a way out of it for them. They're in a cycle of no hope."

Meer, of the Leeds Racial Harassment Project, sees the isolation, prejudices and lack of opportunities taking a toll even on the vast majority of Pakistani youths who don't turn to crime or gangs.

"It's not unusual to see young people facing real mental health issues here," he said. Such programs as the Islam awareness training the organization has done for police, schools and health care providers has resulted in "some progress" but no solutions, Meer said.

Pedaling around the steep streets of Beeston on their BMX bikes, older Pakistani boys glare at the lingering TV news crews and shout obscenities about the war in Iraq, cursing President Bush and Prime Minister Tony Blair before speeding off.

Residents who are willing to talk frankly about race relations in Beeston do so only under the cloak of anonymity, fearful of reprisals.

"I'm really worried," admitted a young mother from Kashmir, coming home from her office job with the power company. "We keep hearing that they're coming for us, that there'll be attacks against Muslims here because of the bombers. We had nothing to do with that!"

A white retiree standing beneath a "For Sale" sign outside his home watched Pakistani teenagers shout obscenities at one another in jest. His wife's baskets of pink fuchsias hung in vain sentry along the wall, unable to camouflage the terrace junkyard next door where junkies often gather.

"You see them dealing drugs all the time -- just look at the late-year BMWs and Mercedes you see around here being driven by these young Pakistanis with no visible means of support. Reporting it does no good. I've had two cars smashed in, people threatening me," the man said.

"They always hide behind the word 'Islam,' but how many Muslims do you see getting stoned out of their minds on vodka and coke, sticking needles in their arm, chasing after young girls. Their parents are decent people who have no idea what their kids have got into."

Two blocks away, the police have raided another house. Boys bicycle up to the new police tape at the end of the street. Neighbors politely ask to duck under to take their groceries home. People sit on their stoops as the plastic sheeting goes up again. There is nothing to see anymore, but still they look.

The Leeds Grand Central Mosque, at right in background, forms part of the skyline of the majority-white city, where 75 nationalities live side by side. At 4.5 percent of the population, South Asians and their British-born children form the largest minority group in the city of 715,000.