Hoping to calm nervous commuters, London Mayor Ken Livingstone took the underground to work. But at the King's Cross Station, near the site of Thursday's deadliest explosion, police briefly evacuated commuters after finding an unattended object in the street.
Nothing dangerous was found, and the station was reopened. Investigators say preliminary evidence indicates the attacks were not carried out by suicide bombers, because they believe timing devices were used. In Parliament, Prime Minister Tony Blair said the attacks were probably the work of Islamic extremists. "We express our revulsion at this murderous carnage of the innocent. We will pursue those responsible, not just the perpetrators, but the planners of this outrage wherever they are, and we will not rest until they are identified, and as far as is humanly possible, brought to justice."
Meanwhile, mourners in London paid their respects to victims of the attacks. Some came to lay flowers near where one of the bombs destroyed a double-decker bus. At City Hall, Mayor Livingstone led religious leaders and other dignitaries in signing a book of condolence messages. He wrote: "The city will endure."
A temporary mortuary has been set up to receive bodies from the four bomb sites. Here, forensic experts will use DNA and other methods to identify the victims. Scotland Yard says it has identified the first of the victims, 53-year-old Susan Levy of Hertfordshire, outside London.
A public vigil is planned for Thursday night in Trafalgar Square, where just one day before the bombings, Londoners celebrated being chosen as the host city for the 2012 Summer Olympics.