London, England (CNN) -- A British judge opens a detailed investigation Monday into the killing of 52 people in suicide bombings on London underground trains and a bus on July 7, 2005.
Justice Heather Hallett will probe whether the secret service or police could have prevented the attacks, by British-born bombers backed by al Qaeda.
She is expected to spend about six months on the investigation, which will also examine the emergency services' response to the blasts that threw London into chaos during the morning rush hour.
The probe -- known formally as a coroner's inquest -- follows criminal and parliamentary investigations, and could not begin until the police investigation was complete.
Two of the bombers, including ringleader Mohammed Sidique Khan, were trailed by security services for a year before the attacks, according to a report released last year by the Parliamentary Intelligence and Security Committee (ISC).
Entitled "Could 7/7 have been prevented?" the report said that domestic intelligence service MI5 considered Khan a "small time fraudster" and "minor criminal" and did not link him to potential attacks within the UK at that time.
John Reid, the home secretary at the time of the attacks, said the four bombers -- three British males of Pakistani descent and a Jamaican-born man -- were young "radicalized" Muslims whose motivation was "fierce antagonism to perceived injustices by the West against Muslims" and a desire to become martyrs.
CNN
