Authorities said the death toll from the July 7 explosions rose to 54, including the four suicide bombers.
Police said two of the attackers were Shahzad Tanweer, 22, who carried the bomb on the subway train that exploded between the Liverpool Street and Aldgate stations, and Hasib Hussain, 18, whose bomb exploded on the double-decker bus, killing 13.
Although British investigators have not released the other two names, news reports identified them as Mohammed Sidique Khan, 30, the father of a baby girl, and Jamaica-born Briton Lindsey Germaine.
The Times of London, quoting unidentified police sources, said detectives were searching for Magdy el-Nashar, 33, an Egyptian-born academic who recently taught chemistry at Leeds University.
He reportedly rented one of the homes being searched in the northern city of Leeds. Neighbors said he recently left Britain, citing a visa problem, according to the Times.
Police searched another address in Leeds Thursday in their hunt for anyone who aided the bombers. Authorities believe the bombers did not act alone and their collaborators or leaders are likely still at large.
“We are as certain as we can be that four people were killed and they were the four people carrying bombs,” London Police Commissioner Ian Blair said, according to the AP. “We don’t know if there is a fifth man, or a sixth man, a seventh man.”
Two claims of responsibility purportedly from militant Islamic groups have surfaced.
Meanwhile, London’s busy streets came to a standstill Thursday as the city paid silent tribute to the victims of the four bombings of the subway trains and bus a week ago.
Office workers filed into the streets, construction workers removed their hard hats and Queen Elizabeth II stood motionless outside Buckingham Palace as a crowd filled Trafalgar Square for two minutes of quiet that began at noon, reported the Associated Press.
The silence was broken only by the tolling of Big Ben.