London (CNN) -- A British coroner will deliver her verdict Friday after a six month inquest into the deaths of the 52 people killed in bomb attacks on London's transport system on July 7, 2005.
The key question facing the coroner, Justice Heather Hallett, is whether any of the deaths, on three London Underground trains and a bus, could have been prevented.
The inquest heard from relatives of victims, survivors, London Underground staff, police and emergency personnel.
But perhaps the most significant witness was a senior figure from the security service MI5, who was asked to account for how it was that two of the four bombers -- three British males of Pakistani descent and a Jamaican-born man -- were photographed as part of a separate terror investigation, but not followed up.
Witness G, as he was known, expressed regret that MI5 had missed the significance of Mohammed Siddique Khan and Shehzad Tanweer, but rejected any suggestion of intelligence failings.
Another key question of Hallett's probe is whether any of the deaths were caused by any delayed reactions of emergency services, due to fears of secondary explosions or over-regulated safety guidelines.
As well as stories of great courage and great fortitude, the inquest heard reports of police officers apparently reluctant to board the wrecked bus on Tavistock Square in central London as badly injured people screamed for help.
There were similar stories of firemen unwilling to enter an underground tunnel until certain it was safe to do so.
Some recommendations from the coroner about the rigidity of procedures by the emergency services are likely, but sweeping criticism is not expected, according to one analyst.
"It's very easy to say in retrospect that people held back and therefore they were cowards," said Jennifer Cole, from think tank the Royal United Services Institute.
"In different situations they might have gone forward into the path of a secondary device and probably would have been martyred heroes but they would have been dead. In the grand scheme of things it's much better that they hold back than go forward and put themselves in danger."
Among the bereaved who took part in the inquest was John Taylor, whose 24-year-old daughter Carrie died on a train approaching Aldgate tube station.
Unhappy with previous explanations of exactly what happened on 7/7, Taylor decided to represent himself at the inquest, listening to harrowing details of his daughter's final moments, and putting questions directly to those who tried to save her life.
The questions he asked, he told CNN, came from the heart.
"The day Carrie came back to Billericay in a coffin I remember sitting in the chapel with [my wife] June and my son Simon and making a promise to Carrie to find out as much as I possibly could," Taylor told CNN.