As investigators struggle to piece together details of the transit attacks in the British capital, police say 49 people are on a list of confirmed casualties that is, unfortunately, expected to grow larger.

London's Metropolitan Police confirmed the growing death toll after commissioner Sir Ian Blair told reporters all 13 victims had been recovered from the bus torn apart by a bomb Thursday morning.

Speaking to reporters on Friday, Sir Blair predicted the toll would exceed 50, once all the dead aboard the tangled subway train wreck at Russell Station had been accounted for. Twenty-two people were in serious or critical condition and many were reported missing, deep inside a subway tunnel near Russell Square.

"We know that there are more than 50 fatalities. There is a great difficulty in determining how many fatalities there are because two of the scenes are very difficult in terms of recovery," Blair said.

In addition to Britons, he said the victims came from at least five countries: Australia, China, Poland, Portugal and Sierra Leone.

One-hundred people were hospitalized overnight, with 22 of those in critical condition, Blair said. In total, more than 700 people were injured in the attacks.

CTV's Janis Mackey Frayer, reporting from London, says officials are proceeding very cautiously with the investigation.

"They are saying that there are still a number of bodies down there. They are also dealing with some structural compromises to the Tube itself, so they're afraid that the tunnel might actually collapse," said Mackey Frayer, referring to the blast that occurred between Russell Square and King's Cross stations.

On the subject of who was behind the attacks, Blair said so far there are suspicions, but no leads.

"They're either at large in the U.K., or at large somewhere else or they're dead," he said, conceding that the timing of the apparently attacks points to more than one perpetrator.

When asked whether there is any truth to reports the bus blast was triggered by a suicide bomber, Blair said there was "absolutely nothing" to suggest it was.

Nor, he added, do investigators have any evidence that can "rule it out."

Wary commuters return

As the probe continues, much of the transit system was reopened under tight security on Friday.

As a result of the heightened vigilance, suspicious packages were reported at several stations throughout the capital.

Euston Station was closed temporarily as emergency services scoured its rail and underground levels. Then, shortly after that station was reopened, the Liverpool Street and Charing Cross underground stations were shut.

Both were subsequently reopened.

Amid such anxiety, it was clear some commuters were reluctant to use the network on Friday.

Aldona Mosjko was among them.

"Normally, I take the bus, but today, I took a taxi. I was a bit afraid," she told the Associated Press.

Usually-packed double-decker buses and subway carriages were less congested than during morning rush hour on other days.

While some dread was evident, many Londoners exhibited a steely resolve to overcome the worst attack on the city since the Second World War, one reminiscent of the stoicism that prevailed under the blitz of the Nazi Luftwaffe.

"Certainly, everyone is using words such as 'resolve' and 'resilience'. While they left their homes with a degree of trepidation, they were determined to show those responsible that the city cannot be brought to its knees," Mackey Frayer said.

The Queen, who spent the day with members of the royal family offering support and condolences to those injured in the blasts, spoke of her admiration for London's resilience.

"Those who perpetrate these brutal acts against innocent people should know that they will not change our way of life," she said Friday at Royal London Hospital.

Thursday's explosions hit three subway stations and a double-decker bus in near-simultaneous attacks, beginning at 8:51 a.m. local time and ended about 40 minutes later when a blast ripped the top off a bus in Tavistock Square in central London.

Body of one bomber possibly found

There are reports that British security officials may have recovered the body of one of the bombers, though this has not yet been confirmed.

Eyewitness accounts say after the driver of the double-decker bus announced that the bus was being rerouted because of police activity, someone was seen on the upper deck fiddling with a bag.

"Everybody is standing face-to-face, and this guy kept dipping into this bag," Richard Jones of Berkshire, west of London, told the British Broadcasting Corp.

Shortly after that, say the witnesses, the explosion went off.

According to Standish, the man may have intended to leave his bomb on the subway, but was unable to board because the system had already been shut down. The man may have gotten on a bus instead and detonated the package sooner than he meant to.

Bombs likely homemade

Meanwhile, police maintain they had neither warnings of the attacks, nor the intelligence to suggest any were imminent.

Britain's domestic intelligence service MI-5 has joined police in a massive search for those responsible for the attacks.

As the manhunt continues, investigators revealed that each of the four bombs contained less than 10 pounds of high explosives, which could be carried in backpacks.

They were placed on the floor of the subway cars and either the seat or the floor of the No. 30 bus, suggesting the attacks were not the work of suicide bombers.

"We have absolutely nothing to suggest that this was a suicide bombing attack, although nothing at this stage can be ruled out," Blair told reporters Friday.

An explosives expert said the bombs were likely crude homemade devices set off with a timer.

Andy Oppenheimer, a weapons expert who consults for Jane's Information Group, said the bombs were probably made from relatively easy-to-obtain plastic explosives; not higher-grade military plastics, which would have been far deadlier.

"Any crook with ready cash could obtain this stuff if they knew where to look for it," Jane's Intelligence Digest editor Alex Standish told the Associated Press.

Forensic investigators, their skills refined by decades of anti-terror work from IRA bombings, are scanning hours of closed-circuit television footage, sifting through tonnes of debris, and examining traces of explosives.

So far, the inaccessibility of one of the wrecked trains, which lies 70 feet below street level, is making it difficult for investigators to obtain detailed forensic information on the bombs.

'Lots of leads'

Blair said no arrests have been made so far, but officials have "lots and lots" of leads.

In a statement posted Thursday on a website, a group calling itself the Secret Organization of al Qaeda in Europe said it staged the blasts in retaliation to British involvement in Iraq and Afghanistan.

In Washington, counterterrorism officials said they were taking the group's claim seriously.

In London, Britain's top law enforcement official, Home Secretary Charles Clarke, said Friday that authorities were investigating the website, but had not verified its authenticity.

"Their claim is something we certainly take seriously," he told British Broadcasting Corp. radio.

Clarke said he couldn't say for sure whether the bombers were Muslim terrorists.

"It's very possible that that was the case, but we haven't ruled out other forms of terrorist attacks," he said.

Security analysts also say the blasts bore similarities to last year's Madrid bombings, when 10 bombs hidden in sports bags exploded on four packed commuter trains, killing 191 people during rush hour.

A U.S. law enforcement official said authorities had vague information from Abu Farraj al-Libbi, reputedly No. 3 in the al Qaeda terror network, that al Qaeda was seeking to mount an attack similar to the Madrid bombings.

But Standish points out that al Qaeda is a different terror network than the one that launched the terror attacks of Sept. 11, 2001.
Then, leaders commanded a more hierarchical, organized collection of cells.

"Al Qaeda is now an ideology. It's moved beyond being a structural organization," said Standish, adding those responsible for the London attacks may have been British citizens with no formal terrorism training or direct links to al Qaeda commanders.

That kind of loose grouping is far harder to battle than a more tightly knit, organized group.