Ian Blair (file photo)
The commissioner said Thursday that anti-terrorism police are still trying to determine how many people were involved in the failed attacks on three subway trains and a bus.
Earlier today, British police arrested nine more people - none of whom they believe to be among the three suspected bombers still at large.
Detectives are questioning the one suspected bomber they arrested early Wednesday in the central English city of Birmingham.
Police say Yasin Hassan Omar, a Somali who has been living in Britain since 1992, fled from the Warren Street subway station in London on July 21 after a hidden bomb failed to explode there.
Some information for this report provided by AFP and Reuters.