LONDON - A second wave of bombings echoed through London's transit system yesterday, shutting down much of the city for hours and leaving commuters and residents jittery with fears that a sustained campaign of violence may be under way.
One person was reported injured in what police described as "an attempt" by bombers to explode bombs on three subway trains and a double-decker bus, the same number and types of targets that were struck by suicide bombers July 7 in attacks that killed 56 people and injured more than 700.
Police said last night that they arrested two people in the vicinity of the trains that were targeted, but they released one person without charges and privately cautioned that there was no evidence connecting the other man to yesterday's incidents.
"Clearly, the intention must have been to kill," Ian Blair, the police commissioner who oversees Scotland Yard, said of yesterday's attacks. "You don't do this with any other intention."
Yesterday, as two weeks earlier, thousands of commuters fled the Underground trains in terror, women leaving behind shoes, men leaving behind briefcases as they sought safety above.
Only this time, no mangled trains or mangled bodies were left behind on the subway system, known to Londoners as the "Tube."
Three million passengers ride the subway each weekday; 6 million take London's vast network of buses.
Caroline Russell, 42, said she and other passengers smelled what seemed to be burning rubber deep underground on the Victoria Line. When the train stopped at the Warren Street station, in North-Central London, she said, a rush of panicked passengers from another car on the train began running for the exits.
"There was just a stampede, with people running, crying, really upset," she said. "We all moved to a parallel tunnel, and I knew we had to get out of there, and then this Italian girl who was all by herself collapsed at my feet."
Speaking to another passenger once she helped the Italian girl to street level, Russell said, she learned from a passenger on another car that a backpack being carried by a young man had "exploded but not real loudly." Passengers from that car pulled the emergency cord and then ran through connecting doors into another car while the train was moving toward Warren Street.
"We were all shaken," she said. "But we all felt fortunate."
Police were releasing few details about the attacks, but witnesses reported hearing relatively low-level explosions beginning about 12:25 p.m., and London's subway system was evacuated.
Not all of the bombs exploded, the commissioner said, and he left unclear whether only detonation devices may have gone off or whether bombs that may have exploded were simply not powerful enough to do serious damage. Last night, bomb squads were on hand in Hackney, where an explosion on the No. 26 bus blew out several windows.
The BBC, citing intelligence officers, reported that the recovered explosives were similar in makeup to those used in the July 7 attacks.
A shaken city
Police with high-powered weapons were on streets where normally only unarmed bobbies are seen, emblematic of how London, despite residents' efforts to get on with their lives, remains a city shaken by two series of attacks in as many weeks.
The London Eye, the giant Ferris-wheel-like attraction on the River Thames, was emptied of its passengers and closed. The U.S. Embassy turned away afternoon appointments.
Large expanses of London's streets, usually with bumper-to-bumper traffic during the noon hour, were closed to traffic, which diverted into miles-long traffic jams elsewhere, blue and white barrier tape snapping in the wind.
Office buildings were evacuated. Pubs were emptied. People stood on sidewalks and in the closed streets asking one another for information and seeking ways to get home.
Police and Mayor Ken Livingstone asked anybody with information to come forward.
And at Downing Street, Prime Minister Tony Blair again appealed for calm even as, in the early hours of the incident, the police commissioner went on television and told Londoners to "stay put."
"We can't minimize incidents such as this," Blair said at a news conference with the Australian prime minister at 10 Downing St. "They're done to scare people, to frighten them and make them worried."
Yesterday's incidents were an echo of those that killed and maimed so many two weeks ago to the day. Like then, three subway lines and a double-decker bus were targeted yesterday. Like then, the pattern of the targets yesterday spread north, south, east and west.
Like those of two weeks ago, yesterday's attacks left thousands of people scurrying to ground, many of them shaken and in tears, and some trying to reach friends and family they feared may have been lost to the violence.
Sniffer dogs and firetrucks were everywhere. Emergency workers in puffy chemical suits hopped out of rescue vehicles. Emergency sirens howled throughout the city.
And, like those of two weeks ago, yesterday's attacks came without warning.
"That's the frightening part, the not knowing, which makes you feel quite helpless," said James Hannington, 39, who had been selling flowers inside the Shepherd's Bush Tube station. "How do you protect yourself on the Tube if someone is willing to set off a bomb?"
That has been the question here since long before the bombs exploded two weeks ago.
Londoners had been warned by authorities that an attack on the city was "inevitable," but with 3 million people passing through Tube turnstiles, the only line of defense has been for intelligence officials to stop potential bombers before they carry out attacks and for passengers to heed pleas to be vigilant about abandoned packages and suspicious riders.
Police said they would again be scanning tapes from closed-circuit television cameras in hope of identifying who was responsible.
Authorities first believed that one attacker had fled to University College Hospital and was hiding inside. Armed police searched the building for at least two hours before announcing it clear of suspects.
Sky News TV had reported that police were searching for a man with wire protruding from a blue shirt.
One of the men in custody last night was arrested near Downing Street, site of the prime minister's residence and office, and the other - who was later released - near Tottenham Court Road, which is near the Warren Street subway station, where one of the incidents took place.
Earlier in the day, television showed police pointing high-powered weapons at a man carrying a backpack near Downing Street. Police said at the time that they did not believe he was connected to the attacks.
The Associated Press reported that President Bush was briefed on the explosions and said the attackers "understand when they kill in cold blood it ends up on our TV screens, and they're trying to shake our will. And they're trying to create vacuums in which their ideology can move."
Higher alert in U.S.
Mass transit systems in the United States have remained on higher than usual alert since the London bombings two weeks ago.
In New York, Mayor Michael R. Bloomberg said police will begin conducting random searches of packages and backpacks carried by people entering the city's subway, the AP reported.
The attacks in London targeted trains near the Warren Street, Oval and Shepherd's Bush stations and the No. 26 bus on Hackney Road in East London.
Stagecoach, the company that operated the stricken bus, said the driver heard a bang and went upstairs, where he found the windows blown out, according to a release from the company. It said that the bus was structurally intact and that there were no injuries.
July 7 attacks
Yesterday's incidents came as focus in the search for clues in the July 7 attacks seemed to be on Pakistan, where three of the four bombers had visited shortly before then.
A previously unknown group calling itself the Secret Organization of al-Qaida in Europe had claimed responsibility for the July 7 attacks. Officials have not confirmed the group's existence or whether it was responsible.
The group had said the attacks were in response to Britain's alliance with the United States in Afghanistan and Iraq.
Scott Gerwehr, an expert on the psychology of terrorism with the Rand Corp. in Santa Monica, Calif., said the second attack, so close to the first, did not surprise him.
"What the actual research shows, and this isn't just me opining, is that you'll find that what we call terrorism is just another kind of effort at mass persuasion, but it uses violence," he said. "A follow-up attack is to increase the impact and the effect. If you believe the earlier claims that this is about Iraq, this second attack is textbook."
He said, though, that when attacks become too frequent, they become less effective and often result in a "stiffening of the spine" of those being targeted.
And much of how Londoners respond will be determined, he said, on how the government responds. If arrests are made and progress is shown in finding those responsible and preventing attacks, Londoners are likely to remain resolute in allowing only minimum disruptions in their lives, Gerwehr said.
Yesterday, as after the first attacks, most Londoners seemed intent on doing just that.
Within hours of streaming up to the street seeking safety, thousands of commuters were streaming back underground and back onto the trains.
"I've kind of been scoping people out, looking at them and at their bags," Rachel Stallworthy, 25, said after taking the Central Line to Shepherd's Bush within hours of that station and others being evacuated. "First, there's no other way for me to get around. Second, do we really want to allow these people to shut down the city?"
"It's a bit scary," conceded Guido Sanzio, 39, who had just taken the Central Line from his job in London's financial district back to his home in Shepherd's Bush.
"I'll be back on the Tube tomorrow. They haven't hit one of my trains yet, but who knows how long I'll be able to say that?"