Police: 'Lots And Lots' Of Leads

Police said Friday that the bombs used in London's terrorist attacks held less than 10 pounds of explosives each — light enough to easily tote in a bag or knapsack.

Police also said they had uncovered no evidence suicide attackers had set off the explosions, but stressed they were still in the early stages of what promises to be an arduous investigation.

Law enforcement officials declined to respond to questions about a U.S. official's statement that evidence indicating timers were used was found in the debris. London police also played down the possibility the devices were detonated by remote control using cell phones, instead asking the public for patience Friday as their investigation picks up momentum.

CBS News Correspondent Jim Stewart reports

Stewart reports investigators now suspect all the bombers used what they called the "step-on, step-off" delivery system of dropping off a bag and quickly leaving.

Whoever placed the bombs put them on the floor in three Underground cars, and either on the floor or on a seat of one of London's red, double-decker buses, the city's police commissioner said at a news conference.

"We have absolutely nothing to suggest this was a suicide bombing attack although nothing at this stage to rule that out," Sir Ian Blair, commissioner of the Metropolitan Police, said.

Police said they had found no bombs other than the four that exploded. Police destroyed two suspicious packages in other areas in controlled explosions, but Blair said they turned out to be harmless.

Media reports of additional explosives could be attributed to the initial confusion about the number of bombs, said Assistant Commissioner Andy Hayman.

"Initially, the forensic investigation suggests that each device used had less than 10 pounds of high explosives," Hayman said. The weight of explosives was smaller than recent bombs detonated in the Middle East.

Hayman appealed for patience as the investigation proceeds.

"Our people are working under the most extreme circumstances," he said — including amid fears that the tunnel will collapse on top of them at the blast site near the Russell Square tube station, where bodies lay uncollected a day later as engineers studied the area.

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

How the bombs were detonated remained an open question Friday.

A U.S. law enforcement official said Thursday that investigators believe some of the bombs were on timers, based on evidence recovered from the rubble. The official, who spoke on condition of anonymity because the investigation is ongoing, would not further describe the evidence and London police declined to comment on the statement.

Blair confirmed that police considered shutting down London's cell phone networks Thursday as the explosions were reported, apparently out of concern the bombs were detonated by mobile phone, but ruled it out.

"We did consider it. We do have that ability," Blair said. But he said commanders considered how that would affect public confidence, and decided not to do it.

Moreover, investigators doubt that cell phones — used in the Madrid train attacks a year ago — were used to detonate the bombs in the Underground because the phones often don't work in the system's deep tunnels, London's transport police said Friday.

Police also found no evidence suicide attackers had acted as human detonators for the explosives they carried — but conceded their work was just getting started.

Investigators were sifting through wreckage, poring over hours of closed-circuit TV footage and interviewing witnesses to find answers behind the deadliest attacks the city has seen since World War II. The process could take months.

"Consider the number of routes, the number of scenes, the opportunities which they present, and which is then complicated further by a bus that is moving," Hayman said of tracing the attackers movement on surveillance tapes.

Police said determining the type of explosive device might help. So far, officials have said the explosions had all the signatures of an attack from Osama bin Laden's al Qaeda terror network.

In Washington, current and former American counterterrorism officials said they were taking seriously an Internet claim by a little-known group calling itself "The Secret Organization of al Qaeda in Europe" that it staged the attacks.

They were trademark al Qaeda: near-simultaneous explosions, using improvised devices, aimed at Westerners, according to the officials, who spoke with The Associated Press on the condition of anonymity because investigations were ongoing.

Little was known about the group, which also claimed responsibility for the last major terror attack in Europe: a string of bombs that hit commuter trains in Madrid, Spain in March 2004, killing 191 people.

Among theories investigators are pursuing is whether the group may be linked to Iraq's terror chief, Abu Musab al-Zarqawi.

In Baghdad, the chief government spokesman said Friday that Islamic extremists have been using Iraq as a planning center for attacks around the world since losing Afghanistan as their base in 2001.

Speaking about the London attacks, Laith Kubba said "we don't know exactly who carried out these acts but it is clear that these networks used to be in Afghanistan and now they work in Iraq."

The spokesman said that insurgents in Iraq and those who carried out the London attacks "are from the same network. There are different groups in the world, but they all follow the same school."

Britain's Home Secretary Charles Clarke, whose department is in charge of police and security, said there is a "strong possibility" that a group linked to al Qaeda was responsible for the attacks. But he stressed that it was premature to draw conclusions about the identities of the attackers.

More than a half-dozen current and former intelligence officials interviewed Thursday conceded that al Qaeda in Europe was a new name to them. But others said it could be an existing group, seeking notoriety with a brutal attack and new title.

Dozens of people died in the four bombings, although police continued to work to establish the precise number because investigators had not been able to reach all the dead inside the tunnel and in the twisted wreckage of the double-decker bus, peeled open on the top and sides by the bomb.

"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.

"One is the bus which is taking some time because of the nature of the explosion, but more acutely the tube train at Russell Square still contains a number of bodies which have not yet been retrieved, we do not know how many there are there," he said.