LEEDS,(AP)- New evidence suggests four suicide bombers, including at least three Britons of Pakistani descent, carried out the terror attacks in London, officials said. Surveillance cameras captured the men as they arrived in the capital 20 minutes before the explosions began.

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.

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 &#34bomb factory&#34 during the Leeds raids, the newspaper said.

Police did not identify the four suspects.

Press Association said the men had driven a rental car to Luton, 50 kilometers (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, U.S. President George W. 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, Clarke said &#34strong forensic and other evidence&#34 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. &#34The 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,&#34 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.

Acting on six warrants, British soldiers blasted their way into an unoccupied Leeds row house. Streets were cordoned off and about 500 people were evacuated. Hours earlier, police searched five homes elsewhere in the city. Police still weren”t letting the evacuees return to their homes early Wednesday.

Mohammed Iqbal, a town councilor who represents the City-on-Hunslet section of Leeds, told AP that all of the homes raided belong to &#34British citizens of Pakistani origin.&#34

Three of the homes were in the neighborhood he represents, Iqbal said in a phone call with AP”s office in Islamabad, the Pakistani capital. He said he had just met with police about the investigation. &#34This is not good for Muslims,&#34 Iqbal said. &#34We have businesses here. There will be a backlash.&#34

Several officials, including Foreign Minister Jack Straw, have said the attacks bore the &#34hallmark&#34 of al-Qaeda, and one of the questions investigators are presumably trying to answer is whether the four suspects had outside help in planning the attacks. Jeremy Shapiro, director of research at the center on the United States and Europe at the Brookings Institution, said Europeans had been involved in suicide attacks in the Middle East, but he knew of no successful suicide bombings in Western Europe previously.

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 10p.m. Thursday, and some of his property was found on the double-decker bus in which 13 died, Clarke said. &#34We have now been able to establish that he was joined on his journey to London by three other men,&#34 he 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 20”s fiddling anxiously with something in his bag. &#34This 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,&#34 said Richard Jones, 61, of Bracknell, west of London. &#34He must have done that at least every minute if not every 30 seconds.&#34

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.

Investigators also found personal documents bearing the names of two of the other men near seats on the Aldgate and Edgware lines. Police did not identify the men.

Leeds, about 270 kilometers (185 miles) north of London, has a population of about 715,000. About 15 percent of the residents are Muslim, and many come from a tight-knit Pakistani community, mostly from Mirpur, south of Islamabad in Pakistani-controlled Kashmir. Other pockets of the community are mostly Arab.

Khalid Muneer, 28, a spokesman for the Hyde Park Mosque in Leeds, said the community was surprised by the raids and police claims that the bombers may have come from there. &#34That connection would surprise us all, even shock the whole community. We still think it”s too early to say,&#34 he told AP, adding that Muslims in the area were not opposed to Britain. &#34I”ve seen no calls in this area for jihad against British or American forces. You will not get that sentiment expressed around this mosque.&#34

Police said their investigation was moving ahead, and warned that the death toll would continue to rise. Fifty-six people remained hospitalized Tuesday. Forensics experts have said it could take weeks to identify the bodies, many of which were blown apart and would have to be identified through dental records or DNA analysis. Investigators say 11 bodies have been identified.