Inquests into the deaths of 56 people in London's July 2005 suicide bombings will probe alleged failings by police and MI5 intelligence before the attacks, the coroner conducting the hearings said on Sunday.
Judge Heather Hallett also ruled that inquests into four suicide bombers would be held separately from those of the 52 victims, a relief to families who had protested plans to hold the inquests together.
The suicide bombers set off near-simultaneous explosions on three London Underground trains and a double-decker bus on the morning of July 7, 2005, in what has become known as 7/7, nearly four years after the 9/11 attacks in the United States.
Hallett, giving details of arrangements for the inquests due to start in October, said they would probe what police and MI5 officers knew ahead of the shock attacks.
"The scope of the inquest into the 52 deaths will include the alleged intelligence failings and the immediate aftermath of the bombings," she said.
"To my mind it is not too remote to investigate what was known in the year or two before the alleged bombings. Plots of this kind are not developed overnight," she added.
Janine Mitchell, whose husband Paul survived the King's Cross explosion, welcomed the decision to probe MI5's role.
"We have been very concerned that there were serious failings and it seems that this is the case... We are relieved that someone independent of Government is going to examine what happened.
"We put all our faith in the coroner to do that, so if anything did go wrong it can be fixed."
Hallett also announced that the inquests will not be held with a jury, and that the hundreds of people injured in the attacks will not be designated "interested person" status --granting the right to cross-examine witnesses.