LONDON - Police radically revised the timing of the deadly blasts that tore through the London Underground, saying Saturday that the bombs were detonated just seconds apart - not 26 minutes as first reported.
The explosions were so intense that none of the 49 known dead has yet been identified.
Many bodies still lay buried in a rat-infested subway tunnel and frantic relatives begged for word about others still missing in the worst attack on London since World War II. Police indicated as many as 50 additional victims were unaccounted for.
In a sign of the continued state of alert, police evacuated 20,000 people from Birmingham's central entertainment district Saturday night after intelligence indicating a "substantial threat," said Stuart Hyde, assistant chief constable of West Midlands Police.
He said the alert was not likely connected to the subway and bus bombings. A controlled explosion to disarm a suspicious object was carried out on a Birmingham bus, and officers concluded there was no explosive device.
Deputy Assistant Police Commissioner Brian Paddick said the near-simultaneous nature of the attacks Thursday indicated timers - not suicide bombers - set off the explosions. He cautioned, however, that the investigation was in an early stage and nothing had been ruled out.
Investigators also said the bombs that brought the British capital to a standstill were made of sophisticated high explosives. Investigators said it was too early to pinpoint where the terrorist bombers got the ingredients.
Investigators repeated their assertion that the bombings bore the signature of al-Qaida, the terror network blamed for the Sept. 11 attacks on the United States. The organization, headed by Osama bin Laden, has gained a reputation for sophisticated timing in its terror strikes.
"It will be some time before this job is completed and it will be done with all the necessary dignity to the deceased," said Andy Trotter of the British Transport Police.
Mustafa Setmarian Nasar, the alleged mastermind of last year's Madrid railway bombings, who also goes by the name Abu Musab al-Suri, has emerged as a suspect in the London attacks, according to unidentified investigators cited in The Sunday Times, The Sunday Telegraph and the Mail on Sunday.
Nasar, a Syrian fugitive, allegedly played a key role in setting up an al-Qaida structure in Spain and was indicted there in connection with the Sept. 11, 2001, attacks in the United States. Last year, the U.S. offered $5 million for information leading to his arrest.
Transit officials originally said Thursday's blasts occurred over a 26-minute span, but computer software that tracked train locations and electric circuits subsequently determined the first blast shattered the rush-hour commute at 8:50 a.m in Aldgate station, east London, with the next two erupting within 50 seconds.
A fourth explosion tore through a double-decker bus near a subway entrance, killing 13 people, nearly an hour later. The attacks hit as President Bush and other G-8 leaders were holding a summit in Scotland and a day after London was named the host city for the 2012 Olympics.
Scotland Yard has declined to issue a list of people unaccounted for. Police said Saturday they were looking into more than 1,000 missing-person reports, although they do not believe more than 50 of them are connected to the bombings, suggesting the death toll will remain below 100.
More than 20 people injured in the blasts remained in critical condition, and an unknown number of bodies remained in the Russell Square subway tunnel, where heat, dust and dangerous conditions slowed crews trying to reach the corpses. Many London subway lines run more than 100 feet below ground.
"It is a very harrowing task," said police detective Jim Dickie. "Most of the victims have suffered intensive trauma, and by that I mean there are body parts as well as torsos." Many of those who worked to recover bodies had done the same work during December's devastating tsunami in the Indian Ocean.
Forensics experts were relying on fingerprints, dental records and DNA analysis to identify the victims.
Riders were returning to Underground stations, but warily and in smaller numbers.
"There's just less people," student William Palmer, 23, said at the Chancery Lane subway stop. "Everyone's looking around a little bit more."
The system was set for its first real test on Sunday when 20,000 cricket fans were expected to travel to the British capital for a match between England and Australia.
When asked about the claim of responsibility by a group calling itself The Secret Organization of al-Qaida in Europe, Prime Minister Tony Blair told the BBC on Saturday it was "reasonably obvious that it comes from that type of quarter."
Little was known about the group, but its name was attached to an Internet statement that claimed responsibility for the Madrid commuter train bombings that killed 191 people in March 2004, the last major terror attack in Europe.
A second claim appeared on a Web site Saturday, this one signed Abu Hafs al-Masri Brigades, a group whose name invokes the alias of Mohammed Atef, bin Laden's top deputy who was killed in a U.S. airstrike in Afghanistan in November 2001.
But terrorism experts said the group had no proven record of attacks, and noted it had claimed responsibility for events in which it was unlikely to have played any role - the 2003 blackouts in the United States and London that resulted from technical problems, for example.
A government-prepared dossier, drawn up by the British Home Office and Foreign Office after the March 2004 train bombings in Madrid, Spain, said al-Qaida is targeting middle-class Britons to join its ranks, The Sunday Times reported.
"Extremists are known to target schools and colleges where young people may be very inquisitive but less challenging and more susceptible to extremist reason/arguments," the report says, according to the Sunday newspaper.
At King's Cross station, near the site of the deadliest of the three subway bombings, service was partially restored on Saturday. Flowers and sympathy cards were piling up outside to honor the 21 known dead as the train was bombed between King's Cross and Russell Square stations.
A group of Muslims held a peaceful vigil outside St. Mary's Hospital on Saturday in solidarity with victims.
"We must remember that terror is all around us these days, that terror has no homeland or nationality and no religion and that we all face the same problems together," said Iman Hassan Ali, from the Dar Al Islam Foundation.
"We all want to understand these incidents and today we are here to give our support to the victims and say that we will stand together despite terrorism."