Police: Investigation 'Moving at Great Speed'

London police said they were still trying to determine whether the four men believed responsible for last week's terror attacks had died in the bombings.

"We are trying to establish if they all died in the explosions," Deputy Assistant Commissioner Peter Clarke, the head of the Metropolitan Police Service's (search) anti-terror unit, said in a Scotland Yard press conference Tuesday. He said one arrest had been made in the investigation.

Sky News, a sister network of FOX News, reported Tuesday that all four men — each armed with a separate bomb — perished in the blasts, which killed at least 52 people. The network quoted police sources.

The latest development backs the theory that the attacks were carried out by homicide bombers. There had been initial speculation that the explosives were detonated remotely, with timing devices.

Meanwhile, the BBC reported that explosives were found in a car at a rail station in Luton, 30 miles north of London. Police said earlier they carried out a controlled explosion on a car that was parked at the station and believed linked to the attacks. Metropolitan Police officers from London examining the car carried out the controlled explosion, Bedfordshire police said.

Clarke said one man has been arrested in West Yorkshire and would be brought to London for questioning in the investigation. Six search warrants have been issued at various locations, including the residences of three of the four men.

Clarke told reporters that the four men arrived in London by train about 8:30 a.m. on July 7, about 20 minutes before the blasts began. Closed-circuit TV video captured them arriving at King's Cross Station (search).

Clarke also said that personal documents belonging to three of the four men have been recovered near the sites of the explosions. One of the four was reported missing the day of the attacks by his family.

"This investigation is moving at great speed," Clarke said.

Clarke said at least three of the suspected bombers came from the West Yorkshire region, which includes Leeds — a northern city with a strong Muslim community.

Clarke said police had "strong forensic and other evidence" that the man believed to have carried a bomb onto the subway train that exploded between the Aldgate and Liverpool Street stations died in the blast, and they were awaiting confirmation from the coroner.

One of the suspects had been reported missing by his family on Thursday, and some of his property was found on the double-decker bus in which 13 died, Clarke said. The family said the man had traveled to London with three other men.

Some witness accounts suggested the bus bomber may have blundered, blowing up the wrong target and accidentally killing himself. Media reports have quoted an eyewitness who got off the crowded bus just before it exploded as saying he saw an agitated man in his 20s fiddling anxiously with something in his bag.

"Everybody is standing face-to-face and this guy kept dipping into this bag," Richard Jones, 61, of Berkshire, told the BBC.

One theory suggested the attacker may have intended to leave his bomb on the subway but was unable to board because his coconspirators had already shut the system down.

The U.S. State Department also confirmed the identity of the American citizen who died in the attacks.

State Department spokesman Tom Casey confirmed Tuesday that the American believed killed in the London bombings was Michael Matsushita.

He declined to give any other information but said he could release the victim's name because Matsushita's family had already gone public with it.

"Our condolences go out to his family and his loved ones for their loss," Casey said. "We are continuing to work, both through our embassy and here in Washington, to try and absolutely ascertain the facts of this case."

The family of Matsushita, a New Yorker who moved abroad in the spring of 2001, had already said it was likely he was dead. The 37-year-old left home Thursday to go to work and never returned.

"At this time, we've been told that there is virtually no possibility that he is alive," said David Golovner, a family spokesman. "We realize the police wouldn't have told us that unless they were certain. We have given up, basically, any sort of extravagant theories about how he might still be alive."

Earlier Tuesday, authorities detonated explosives while raiding one of several residences in northern England as sources said police in London identified the body of the bus bomber.

Neighbors of one of the five houses being searched near Leeds told Sky News that a 22-year-old man who lived there with his family went missing last week.

Also Tuesday, FOX was told that a parking lot at a train station in Luton (search), 30 miles north of London, was cordoned off and a car was being investigated in connection with last week's bombings.

Officials said the car would be taken to a secure location after a search.

Further raids were also expected later Tuesday in London, according to police sources who spoke to FOX and Sky News on condition of anonymity.

Sky News said the Leeds raids began after police identified the bomber of the No. 30 bus, which exploded at Tavistock Square last Thursday.

Streets were cordoned off and about 500 people were evacuated from the rundown site of modest row houses in Leeds, 185 miles north of London, police said. Hours earlier, police searched five residences elsewhere in the city as part of the investigation of Thursday's subway and bus bombings.

The military carried out a controlled explosion at 11:30 a.m. so detectives could enter a home in the Burley neighborhood, police said. Ministry of Defense spokesman Charles Morton said an army bomb squad had participated.

No one was inside the house at the time, said police Inspector Miles Himsworth. Detectives were scouring it for explosives and computers, he said.

"It's a very, very complicated investigation," he said. "It will be a very slow and very meticulous search in order that any evidence that is there can be gathered carefully."

Cordons kept bystanders about 100 yards away from the site and police helped make arrangements for prayers scheduled at a nearby mosque to be moved to other mosques nearby, Himsworth said.

Just a few miles away, police had earlier raided five homes. Britain's Press Association news agency reported another house was being searched in the town of Dewsbury, just south of Leeds, but police refused to comment on whether that was linked to the bombing investigation.

Metropolitan Police Commissioner Sir Ian Blair declined to give details about the raids, which began about 6:30 a.m.

"There have been a series of searches carried out in Yorkshire. Those searches are still going on. There's very little else I can say at the moment, but this activity is directly connected to the outrages on Thursday," he told BBC radio.

Metropolitan Police described the raids as part of an "intelligence-led operation."

Prime Minister Tony Blair (search) promised authorities would hunt relentlessly for the bombers. Police said their painstaking investigation was moving ahead, and warned that the death toll, which went from 49 to 52 on Monday, would rise. Some 700 were injured in the attacks; 56 of those remained hospitalized.

Blair went to City Hall on Tuesday and signed a book of condolence for the victims, his office said.

"With deep condolences for all those who lost their lives and for their families who mourn and with heartfelt admiration for London, the greatest capital city in the world," Blair wrote.

The families of those missing since the bombings endured an agonizing wait for word of the fate of their loved ones.

"I need to know, I want to protect him," said Marie Fatayi-Williams, who arrived from Nigeria to find out what happened to her immigrant son, Anthony, 26. "How many tears shall we cry? How many mothers' hearts must be maimed? My heart is maimed at this moment."

The names of two more victims were released Tuesday. The families of 30-year-old financial adviser Jamie Gordon and Philip Stuart Russell — whose 29th birthday would have been Monday — said the two men were on the No. 30 bus that exploded near Tavistock Square (search).

So far, the names of four of the dead have been released.

Forensics experts have said it could take days or weeks to identify the bodies, many of which were blown apart and would have to be identified through dental records or DNA analysis.

Ian Blair said forensic experts were scouring the tunnel where a bomb exploded aboard a Piccadilly line train, the deadliest of the four blasts. Police said they are also scrutinizing 2,500 closed-circuit TV video taken from cameras around the blast sites.

Authorities were analyzing 2,000 phone calls to a hot line and 115,000 calls to police.

"This is the biggest crime scene in England's history," Ian Blair said. "They still have to get underneath the carriages, and it is possible they will find more" bodies.

Help came from abroad, too, as intelligence officials and detectives from some two dozen countries — including Spanish investigators who worked on the Madrid bombings — met over the weekend to discuss leads.

Public transit officials said the number of passengers using London's vast bus and subway network, which handles 3 million people on a typical day, was back to normal Monday.

Sales of bicycles have climbed since the bombings as workers look for alternatives to public transport, the capital's biggest cycle retailer said.

Meanwhile, the U.S. Air Force lifted an order barring its personnel from visiting London because of safety fears following the bombings, a directive that had caused some indignation in the city after it was reported by a newspaper.

The order had applied to Navy personnel as well as the 10,000 Air Force personnel at two major bases in eastern England; the Navy rescinded the order earlier, David Johnson, the embassy's charge d'affaires, told BBC radio.

In contrast, British officials urged Londoners to get on with their lives and not let themselves be overcome by fear.

The Daily Mail newspaper said in an editorial: "We trust the 4 million Americans who come to London each year are made of sterner stuff than the U.S. Air Force."

The Associated Press contributed to this report.