Leeds, England ? New evidence suggests four suicide bombers, including at least three Britons of Pakistani descent, carried out the terror attacks in London, officials said Tuesday. Surveillance cameras captured the men as they arrived in the capital just 20 minutes before the explosions began.

Police raided six homes in Leeds 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.

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

One bomber 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 eight-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 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 a controlled explosion on a parked car, which the BBC reported had 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, Peter Clarke, head of the Metropolitan Police anti-terrorist branch, told a Scotland Yard news conference.

Policemen and an army bomb disposal team member stand near a bomb disposal robot in the Burley district of Leeds, northern England, Tuesday after raids were carried out in the area.

U.S. intelligence agencies are checking the names of the London bombers against their databases looking for any U.S. connection, President Bush told a group of chief executives at a private White House meeting Tuesday.

Tom Noonan, head of Atlanta-based Internet Security Systems, said the president described the bombings as suicide attacks during a meeting with members of the White House’s National Infrastructure Advisory Council, a group of CEOs who provide advice about keeping important networks secure.

Two militant Islamic groups have claimed responsibility for the bombings, which killed at least 52 people on three subway trains and on a bus. Police had previously indicated there was no evidence of suicide bombings, suggesting instead that timers were used.

Although police stopped short of calling them suicide attacks, 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 location 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. We are trying to establish their movements in the run-up to last week’s attacks, and specifically to establish if they all died in the explosions,” 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.