BBC NEWS
Tube bombs 'almost simultaneous'
The three bombs on London underground trains "exploded almost simultaneously", say police.
Scotland Yard said the attacks took place within 50 seconds of each other despite previously saying they had taken place over a longer time period.
British Transport Police have also warned that the recovery of victims could take "days more."
Meanwhile, the government is to announce a two minute silence for 1200 BST on Thursday.
Technical data from London Underground disproved the earlier wider range of timings between explosions, Scotland Yard Deputy Assistant Commissioner Brian Paddick said at a press conference on Saturday.
And there was still no certainty about the number of people whose bodies remain trapped in wrecked train carriages below King's Cross, it was announced.
This would be a "slow, methodical, meticulous process" in very difficult circumstances, said Deputy Chief Constable Andy Trotter.
It would take "as long it takes", he said later.
Missing
There have been 49 confirmed fatalities in the bomb attacks on tube trains and a bus - and concerns remain for a further 25 missing people.
So far no victims have been formally identified - and police warn that the process, due to begin on Saturday, could take weeks to complete.
A 24-hour reception centre has been opened at the Queen Mother Sports Centre in Victoria, central London, to help the families of people not seen since the explosions.
The police say that timings show that the explosions took place at 8.50am - and that the synchronisation could suggest that bombs used in the attack were triggered using timing devices.
High-explosives were used in the attacks and were not home-made, say the police.
Mr Paddick denied reports that investigators were looking "for any specific individual".
Prime Minister Tony Blair warned that security and surveillance will not be enough to stop such attacks - and that there has to be an ideological struggle in which terrorism is "pulled up by the roots".
Speaking on BBC Radio 4's Today programme, Mr Blair commended the "inner resilience" of Londoners - as the capital's transport system began to return to a close-to-normal service. There are now services running on sections of all lines on the London Underground.
A book of condolence has been opened - which was signed by Prince William in Auckland, New Zealand.
Terrorism experts have been arriving from Spain to support the inquiry in London, bringing expertise from the investigation into the train bomb attacks on Madrid.
Forensic search
A claim for the attacks has been made in the name of al-Qaeda - by a group calling itself the Abu Hafs al-Masri brigade.
I saw three bodies on the track - I couldn't look, it was so horrific
Scott Wenbourne
But the BBC's security correspondent Gordon Corera has urged caution over the credibility of the claim.
Forensic teams working in Tube tunnels and at the other scenes of the blasts are taking swabs to try to determine the type of explosives used.
The roof of the number 30 bus, which was ripped off in the blast at Tavistock Square, has been removed from the scene for forensic examination.
Police are also involved in one of the UK's biggest searches of CCTV footage to see if there are any clues as to the identity of the bombers.
BBC security correspondent Frank Gardner said there were a number of key questions which investigators were analysing.
"One of the most important is were the bombers home-grown British terrorists or was this a hit team that came in from abroad?" he said.
One possibility being investigated was that the bomb maker was an expert who came and instructed the bombers.
Another area was to see if they were "linked directly" to what was left of the core of al-Qaeda in Afghanistan and Pakistan or acting alone.
Search for missing
Anxious family and friends are continuing their search for loved ones who have not been heard from since the bombings.
EMERGENCY NUMBERS
Anti-terrorist hotline: 0800 789 321
Missing relatives: 0870 156 6344
The emergency call centre in London has taken more than 120,000 calls from the public.
Those looking for missing people have been contacting hospitals, as well as taking photos and posters to the four blast sites.
Scotland Yard confirmed seven people died in the Liverpool Street explosion, another seven at Edgware Road, a further 13 in the Tavistock Square bus blast and at least 21 at the King's Cross blast. A 49th person died in hospital later.
Some 700 people were hurt, about 69 are being treated in hospital and 15 remain in a critical condition.
Blasts occurred:
Between Aldgate and Liverpool Street tube stations
Between King's Cross and Russell Square tube stations
At Edgware Road tube station
On bus at Tavistock Square
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