British police made an urgent plea to the public on Sunday for all photos, video footage and cell-phone images of last week's bomb attacks here to help catch the killers before they strike again.

Officials told reporters they were not ruling out any theories about the bombers' identities, and they pleaded for witnesses to come forward to help in what deputy assistant police commissioner Brian Paddick called "a painstaking and complex inquiry." They also announced an e-mail address -- -- to which people could send photos and video footage shot during the attacks on three subway trains and a double-decker bus that killed at least 49 people and injured 700 Thursday.

Police said they were ruling out no theories in an investigation that so far appears to have produced few solid clues about who staged the subway attacks, which took place over a 50-second period during the morning rush hour. The bus bombing occurred nearly an hour later.

Earlier in the day police announced they had arrested three men at Heathrow Airport Saturday night and held them for questioning under the Prevention of Terrorism Act. The three -- British citizens who were flying in together from an undisclosed location -- were released late Sunday night without charge after officials said they had found no evidence linking them to the bombings.

Under Britain's anti-terrorism laws, enacted after the Sept. 11, 2001, attacks in New York and Washington, police can hold suspects up to 14 days without charge.

At times, authorities appeared to be sending contradictory signals to the public. On the one hand, police officials encouraged Londoners to treat Monday as the beginning of a normal workweek. "We think by working together we can get London back in business tomorrow," said Andy Trotter, deputy chief constable of the British Transport Police.

At the same time, Charles Clarke, the cabinet minister in charge of internal security, warned that the bombers were still at large. "Our fear is, of course, of more attacks until we succeed in tracking down the gang that committed the atrocities on Thursday," Clarke told the BBC. "That is why the number one priority has to be the catching of the perpetrators."

Officials in Birmingham insisted that the evacuation of the center of Britain's second-largest city Saturday night had been justified by credible intelligence. However, the security threat no longer existed, they said.

Meanwhile, investigators were engaged in a meticulous search of the area around the wreckage of the No. 30 bus that exploded in Tavistock Square, combing a park and surrounding buildings for evidence. But the biggest challenge remained the search for bodies inside the wreckage of the front subway car in the narrow underground tunnel between the Russell Square and King's Cross stations, site of the deadliest of the four blasts.

Police said they were not certain how many dead remained at the site. Rescue workers had removed all the torsos from the car where the bomb exploded but said they feared there might still be bodies underneath wreckage. Also, they said, the car remained full of smaller body parts. "You have hands, you have feet, you have legs, you have organs, and until we can match A with B you're not certain," said a police official who spoke on condition of anonymity.

Although none of the bodies has been officially identified, police said they had informally notified families of those they believed were killed. Only the London coroner can officially confirm a victim's identity.

Police also defended the emergency services against complaints by some witnesses of long delays before rescue workers reached victims in some of the subway tunnels. Peter Zimonjic, a Sunday Telegraph journalist, wrote that it took nearly an hour for rescue workers to reach the train car 100 yards from the Edgware Road station where he and other passengers struggled to aid maimed and dying victims. Passengers could not escape, according to Zimonjic, because debris blocked the tunnel.

"Some were screaming in panic," he wrote. "The platform was visible, only 100 yards down the track. Illuminated by sunlight it looked like heaven, almost within reach. Yet as close as it was, no one could get there."

Despite such accounts, Trotter told reporters: "I think the response was rapid, effective and efficient in these circumstances."

Londoners gathered in churches, mosques and synagogues Sunday for memorial services for the victims. The nation's religious leaders gathered outside Lambeth Palace, home of the archbishop of Canterbury, to issue a joint statement condemning the attacks.

"We stand together now for a further purpose: to express our shared commitment to resisting and overcoming the evil of terrorism," Sheik Zaki Badawi, of the Council of Imams and Mosques, said, reading from the prepared statement. "It is an evil that cannot be justified and that we utterly condemn and reject."

Police comb London's Tavistock Square, where a bus was blown up Thursday less than an hour after explosions on three subway trains.A girl brings flowers to the bus bombing site. The police probe has so far yielded few solid clues as to the bombers' identities.