He landed in Britain as a child of war and famine, a 14-year-old refugee from Eritrea starting a new life in a rich nation. But almost immediately after he arrived in 1992, according to police and news media reports, Muktar Said Ibrahim became a thug.

Photos from his school days show a smiling boy in a natty blue blazer and red-striped tie, but friends mostly remember booze, dope and fights with fists and racial insults flying. Ibrahim and his mates were notorious muggers; before he was 17, Ibrahim had been sentenced to five years in prison for knife-wielding assaults.

There among the convicts, Ibrahim was introduced to radical Islam, according to media reports. He grew his beard and adopted traditional Muslim clothes. He explained his new religious persona to a friend by saying, "I'm taking life a bit more seriously," the Evening Standard newspaper reported.

Seven years later, Ibrahim, 27, has become the suspected ringleader of a gang of four other alleged Islamic radicals, all of them from East Africa, who turned on their adopted country with an attempt on July 21 to bomb London's subway and bus system.

British authorities are attempting to determine whether Ibrahim and his associates, who are now in custody after their homemade bombs failed to detonate, are linked to the July 7 attacks that killed 56 people, including the four presumed bombers, and wounded 700 on the transit system. Authorities are also trying to determine whether the two incidents were isolated or the start of a violent campaign against the British people, perhaps coordinated by al Qaeda.

With the presumed July 7 bombers dead, this jittery country's best hope of finding those answers may lie with a group of angry young men who found inspiration and leadership from a mugger turned holy warrior.

Yasin Hassan Omar, another member of the group, arrived in London in 1992 at age 11. He had tagged along with his sister and her husband, who were fleeing the violent misery of life in their native Somalia. It is unclear what happened to the family after it reached Britain, but media reports here said young Omar was placed in government-sponsored foster care for the next seven years.

In 1999, when he was 18, a government agency determined that he was a "vulnerable young adult" and awarded him a one-bedroom apartment in north London, which he paid for with a weekly government housing stipend. Sometime shortly after that, reports here said, he took in a boarder: Ibrahim.

Few details have emerged about how the young men met, but reports have said that they may have gravitated toward each other while worshiping at the Finsbury Park mosque in north London, which until 2003 was a center of Islamic extremism. Investigators believe the July 21 attackers mixed their explosives in the apartment where Ibrahim and Omar lived. A neighbor told police she had recently seen Ibrahim in an apartment elevator with a stack of cardboard boxes, which he said contained wallpaper stripper.

Friends have recalled Omar as an avid soccer player and an increasingly vocal Muslim who was often seen with Ibrahim in a local gym and coffee shop. After his arrest, a Muslim shopkeeper recounted that Omar had berated him for selling alcohol. The shopkeeper also said: "Two days after September 11, he was coming into my shop praising bin Laden," the Daily Telegraph reported.

The British public first saw Omar in grainy closed-circuit television surveillance photos from July 21 that showed him fleeing after a failed attack on the subway's Victoria Line near the Warren Street station. A neighbor reported seeing Omar and Ibrahim at their apartment later that day.

Omar was arrested in an apartment in the city of Birmingham in central England six days later, immobilized by a 50,000-volt charge from a police Taser gun. He was the first of the men to be captured.

Two days later, a SWAT team seized Ibrahim as he stood in his underpants on the balcony of a London apartment. As a live national television audience watched, he was taken into custody with Ramzi Mohammed, a short, athletic-looking man. Police were apparently brought there by a tip from a neighbor who had seen Ibrahim's picture.

Police allege that Mohammed attempted to blow up a subway car near the Oval station in south London on July 21, while Ibrahim was allegedly trying to detonate a bomb on a double-decker bus. Wearing a sweat shirt emblazoned with "New York," Mohammed managed to escape a group of angry passengers who chased and tried to tackle him.

His brother, Wahbi Mohammed, who is said to be a London bus driver, was arrested that same day at a dwelling nearby. Police suspect he is a fifth conspirator from July 21 who left a bomb in a backpack in a city park. It is unclear why the bomb was left there.

It is also unclear how Ramzi Mohammed and Ibrahim came together, although various witnesses have reported seeing them together in a coffee shop near Notting Hill. But the Mohammed brothers, described in media reports as being from Somalia and in their twenties, shared Ibrahim's passion for radical Islam, according to accounts provided by friends and the imam at their mosque.

Ahmed Dahdouh, imam of the Muslim Cultural Heritage Center in North Kensington, told British reporters that the Mohammed brothers often wore white Muslim robes and were well known for their radical views. They ran a stall in Notting Hill where they distributed Islamic books and pamphlets. Much of the material was reportedly radical, and Dahdouh said they harshly criticized him for his moderate outlook, calling him an "infidel."

"Ramzi and his brother used to come here in the mosque. There were four or five of them in the group. They caused a lot of trouble," Dahdouh told the Times of London newspaper. "They used to pray on their own, as they used to think we were not proper Muslims. In one of my Friday sermons, I once said that Islam forbids terrorism. I recall Ramzi later came up to me and told me, 'Why did you say that? It's wrong.' " Dahdouh said Mohammed was angry and tried unsuccessfully to have him fired.

Five days after the July 21 attacks, Issac Hamdi, also known as Osman Hussain, who is suspected of trying to detonate a bomb in a subway car near the Shepherd's Bush station, boarded a train that took him under the English Channel to continental Europe. The apparent ease with which he left the country has sparked new debate about how strictly Britain should monitor its borders in the era of a largely borderless European Union.

Tracing his cell phone as he traveled through Paris, Milan and Bologna, police eventually tracked the naturalized British citizen, reportedly 27 and born in Ethiopia, to his brother's apartment in Rome. He was arrested there on July 29.

In the days following his arrest, Italian investigators leaked detailed accounts of their questioning of Hamdi -- unlike British authorities, who can face prosecution for disclosing details of an ongoing criminal investigation. According to several accounts published in Italian newspapers, Hamdi identified Ibrahim as the ringleader of the July 21 group.

Hamdi reportedly said that he and Ibrahim met at a gym in Notting Hill, where they worked out and practiced martial arts, and where Ibrahim showed him videotapes of the war in Iraq. He reportedly also said they worshiped together at the Finsbury Park mosque. Hamdi said Ibrahim told him they "had to do something big" in response to the U.S.-led effort in Iraq, in which Britain is the main U.S. partner. He said Ibrahim told him how to make and set off the bomb.

Hamdi, who grew up in Italy and speaks fluent Italian, reportedly told investigators he fled to Rome because he had friends and family there. He also said the July 21 group had no ties to al Qaeda.

Hamdi has repeatedly said the July 21 bombs were not intended to hurt anyone; on Wednesday his Italian lawyer said Hamdi contends that the bombs were made of flour. A British law enforcement official quoted in the Evening Standard dismissed those claims and said the bombs were "intended to kill and maim on a devastating scale."

Despite Hamdi's statements that global networks of Islamic radicals were not involved, a Saudi official confirmed to The Washington Post that Hamdi placed a phone call to Saudi Arabia just before he was arrested, a call first reported in the Daily Telegraph. In addition, the official confirmed a report in the Times that Ibrahim had visited Saudi Arabia in 2003 and told friends he was going there to receive training.

Virtually no details have emerged of the interrogations of Ibrahim, who applied for British citizenship in 2003 and received a British passport in September 2004, swearing allegiance to be "faithful and bear true allegiance to Her Majesty Queen Elizabeth."

It also remains unclear whether the attackers intended to carry out suicide bombings or expected to survive.

A longtime neighbor of Ibrahim, Sarah Scott, told reporters that he recently recounted to her a desire to die a martyr and handed her a pamphlet called "Understanding Islam." It contained a passage that said, "Anyone who says: 'There is no God (worthy of worship) except Allah,' and dies holding to that (belief) will enter Paradise."

"He told me he was going to have all these virgins when he got to heaven," Scott told reporters.

Police said Ibrahim's parents went to a local police station and made a report immediately after seeing their son identified on television as a potential suspect. They said he had left home in 1994 and had not visited them for many months. "He lives alone elsewhere," they said. "He is not a close family member."

Muktar Said Ibrahim arrived in Britain when he was 14.Police arrested Muktar Said Ibrahim and Ramzi Mohammed, two suspects in the July 21 bombing plot, at this west London apartment building.