Police are working urgently to break suspected bomber Yasin Hassan Omar, drawing on years of experience in fighting the Irish Republican Army as they seek clues to help them hunt down at least three other bombers.
But Omar — who was apparently prepared to die for his beliefs — represents a new challenge for British police, who have never before been confronted by suicide bombers on their soil. The 24-year-old Somali Muslim is accused of trying to blow up the Warren Street Tube station last Thursday, but the bomb failed to fully detonate.
Meanwhile, the police chief warned deadly terror cells could strike any time as thousands of officers flooded the transit system, made more arrests and grilled suspects Thursday in their biggest investigation ever. Exhausted police faced their greatest challenge since World War II.
With sleeper cells still thought to be active, it's "a race against time," said Metropolitan Police Commissioner Sir Ian Blair.
Police nabbed a terror suspect linked to the deadly July 7 bombings after he crossed into Zambia from Zimbabwe, a Zambian official said. Authorities also arrested nine new suspects in Britain and kept up interrogations of a captured bomber from the July 21 attacks.
"It does remain possible that those at large will strike again," Blair said. "There are many thousands of police officers trying to ensure the safety of Londoners."
Blair would not say how many of the force's 30,000 officers were on duty Thursday, exactly three weeks since the July 7 bombings — which killed 56 people including four bombers — and one week since the botched July 21 bombings.
But he called it "the largest investigation the Met (Metropolitan police) has ever mounted" and "the greatest operational challenge that the Metropolitan police service has faced since the Second World War."
Separately, the British Transport Police scrambled their largest-ever deployment to patrol the rail network. Though spokesman Simon Lubin refused to reveal how many officers were deployed, he said 1,300 officers in the capital and about the same number across Britain were working longer hours, and some vacations were canceled.
Blair said his officers were exhausted, with some "very tired faces" around Scotland Yard. But they were determined as they hunt for three more men suspected of taking part in the July 21 attack and anyone that might have helped them. Police have 20 people in custody.
Though four bombs only partially detonated on three subway trains and a bus, their failure did not signal a weakening of the terrorists, Blair insisted.
"This is not the 'B' team. These weren't the amateurs. They made a mistake," he said. "They only made one mistake, and we're very, very lucky."
The bombs, made of biodegradable material, had probably weakened by the time of the attack, officials have said.
At a top security London police station, officers interrogated Yasin Hassan Omar, 24, a Somali citizen with British residency who is suspected of carrying out the failed attack at the Warren Street station. Under police guidelines, the interrogation sessions would last for about six hours, with breaks and an attorney present.
Police also arrested nine men in the south London neighborhood of Tooting under the Terrorism Act.
Police said three of them were Turks who lived above a fast food restaurant where they worked selling halal burgers — made with meat slaughtered according to Islamic dietary laws.
The restaurant owner, who gave his name as Ali, declined to identify the men but said they were aged about 26, 30 and 40. The oldest had worked for him for eight years, and the other two started about two months ago, he said.
Six other men were arrested at a home on a street opposite the Tooting Broadway subway station, police said.
"There were about a dozen armed police officers shouting 'Come on out or we'll send the dogs in.' And then I saw one large, older-looking Asian man being led out. He was dressed in a white gown or robe," said Ben Astbury, 25, who watched the raid from his house.
In Zambia, Haroon Rashid Aswat, 31, was in custody after being arrested in the border town of Livingstone, an official there said. Aswat is believed to have been in telephone contact with some of the July 7 suicide bombers.
Also Thursday, Blair was grilled by an oversight panel regarding a shoot-to-kill policy for potential suicide bombers that resulted in the death of an innocent man — a Brazilian electrician police believed was ready to set off a bomb on the subway.
Jean Charles de Menezes' flag-draped casket reached his hometown in Brazil on Thursday. The plain wooden coffin was taken to a church where it will lie until his funeral Friday.
Blair again expressed his regrets for the killing and promised a full independent inquiry at a meeting of the Metropolitan Police Authority.
Police "thought they were dealing with a suicide bomber — and they were running toward him," Blair said. "They were running toward what might have been certain death. Whatever else has happened, that has to be taken into account."
As for the suspected suicide bomber in custody, Yasin Hassan Omar, a Somali citizen with British residency, was arrested in a dramatic raid by dozens of anti-terrorist police and bomb disposal experts on Wednesday in Birmingham, Britain's second largest city.
A police source told CBS News Correspondent Richard Roth that it was a family member who identified Omar from a grainy picture. A tip from the public then led police to Omar's house.
Omar's religious and political convictions could motivate him to stonewall interrogators, but the prospect of a long prison term might prompt him to talk, said Charles Shoebridge, a security analyst and former counterterrorism intelligence officer with London police.
"A potential suicide bomber is prepared to die, and thereby gain benefits such as an immediate entry to paradise," Shoebridge said. "Clearly the prospect of 30 to 40 years in jail, particularly for a young man, might be a different matter. And consequently, it may be that the suspect will consider cooperating with police."
Police rules dictate Omar had to be given eight hours sleep before formal questioning following his arrest at 4 a.m. Wednesday. He will have access to a toilet and washing facilities, and be given two light meals and one full meal in every 24-hour period, as well as liquids upon request.