LEEDS, England - Surveillance cameras captured the images of four men, including at least three Britons of Pakistani descent, who may have carried out suicide attacks in London, officials said after uncovering new evidence.

Police raided six homes in Leeds Tuesday searching for explosives and computer files that would shed more light on what were believed to be the first suicide bombings in Western Europe. They arrested a man, identified by the British news agency Press Association as a relative of one of the suspected bombers.

Britain's Home Secretary Charles Clarke said today that help from European police and intelligence agencies had made "material differences" to the investigation into the bombings.

"The support that we had from international, and particular European, intelligence agencies and police has been first class," Clarke told a European Parliament committee in Brussels, Belgium. "It has made a difference."

A town councilor told The Associated Press that at least three of the presumed suicide bombers were British citizens of Pakistani ancestry.

One was thought to be Shahzad Tanweer, a 22-year-old cricket-loving sports science graduate, and another was a teenager, Press Association reported.

On its Web site, The Times newspaper named Tanweer, as well as Leeds residents Hasib Hussain, 19, and Mohammed Sidique Khan, the 30-year-old father of an 8-month-old baby. The newspaper said police were still trying to identify the fourth bomber.Without citing sources, The Times said the mastermind behind the attacks, as well as the bombmaker, were still thought to be at large. Police found a "bomb factory" during the Leeds raids, the newspaper said.Press Association, citing police sources, said today that police had identified the fourth suspect; no name was reported. Police have not publicly confirmed the identities of any of the suspects.Press Association said the men had driven a rental car to Luton, 30 miles north of London, and then boarded a commuter train to London's King's Cross station. Police closed Luton's train station and carried out nine controlled explosions on a parked car, which the BBC reported contained explosives.Closed-circuit TV video showed all four men arriving at King's Cross by 8:30 a.m. on Thursday, about 20 minutes before the blasts began, said Peter Clarke, head of the Metropolitan Police anti-terrorist branch.U.S. intelligence agencies are checking the names of the London bombers against their databases, looking for any U.S. connection, President Bush told chief executives at a private White House meeting Tuesday.Two militant Islamic groups have claimed responsibility for the bombings, which killed at least 52 people on three subway trains and on a bus.Although police stopped short of calling them suicide attacks, Peter Clarke said "strong forensic and other evidence" suggests one of the suspects was killed in a subway bombing and property belonging to the three others was found at the locations of the other blasts."The investigation quite early led us to have concerns about the movements and activities of four men, three of whom came from the West Yorkshire area," Peter Clarke said.The West Yorkshire region includes Leeds, and the homes of the three suspects from the city were among the six that were searched Tuesday.Mohammed Iqbal, a town councilor who represents the City-on-Hunslet section of Leeds, told AP that all of the homes raided belong to "British citizens of Pakistani origin.""This is not good for Muslims," Iqbal said. "We have businesses here. There will be a backlash."Several officials, including Foreign Minister Jack Straw, have said the attacks bore the "hallmark" of al-Qaida, and one of the questions investigators are presumably trying to answer is whether the four suspects had outside help in planning the attacks.Peter Clarke said police had strong 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 at 10 p.m. Thursday, and some of his property was found on the double-decker bus in which 13 died, Peter Clarke said.Some witness accounts suggested the bus bomber may have blundered, blowing up the wrong target and accidentally killing himself. A witness who got off the crowded bus just before it exploded told AP he saw an agitated man in his 20s fiddling anxiously with something in his bag."This young guy kept diving into this bag or whatever he had in front of his feet, and it was like he was taking a couple of grapes off a bunch of grapes, both hands were in the bag," said Richard Jones, 61, of Bracknell, west of London. "He must have done that at least every minute if not every 30 seconds."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.