Investigators now have a chance to get inside the minds of the five terror suspects, who were last night still being interviewed at Paddington Green police station, and who failed in their alleged mission to bring chaos to London. But many hours of questioning may never extract a satisfactory reason from the men for their motives.
There is one issue on which criminal investigators and psychologists experienced in profiling suicide bombers agree. They reject any suggestion that the bombers were suffering from a form of mental illness because this would have made them unreliable to their recruiters.
Instead, the profile that is beginning to emerge of those who carried out the 7 July bombings and the failed attempt on 21 July is of rational young men acting as trained soldiers, focused on a mission and disciplined not to betray any emotion.
Professor David Canter, who has carried out extensive research into suicide bombers, compares them with "spree killers" - people such as Thomas Hamilton, who carried out the massacres at Dunblane primary school.
"It may be surprising that someone would take their own life," said Professor Canter, who heads the Centre for Investigative Psychology at the University of Liverpool.
"But these individuals know they are going to die. They could be in a state that is close to depression but it is unlikely they would be diagnosed with a mental illness."
Another theory is that the five who failed in their mission on 21 July would have been determined to repeat their mission until they succeeded. The extensive research which has already been published into the motivations of suicide bombers suggests that those who fail in their mission feel shame and frustration. .
Elie Godsi, a consultant clinical psychologist, says that there is a huge stigma attached to terrorists who fail which means they are unable to return to their communities.
"There is a great deal of stigma in having not succeeded," said the forensic psychologist from the University of Nottingham and author of Making Sense of Madness and Badness. "They will regroup and try again or try to take their own lives."
Social backgrounds are a factor, although experts warn that it is misleading to say that all terrorists are no-hopers from deprived communities. There is likely to be a distinction between those in custody at Paddington Green police station in London and those who planned the attacks.
An internal dossier from M15, leaked to newspapers, identifies the planners as usually educated, often with degrees in engineering or information technology, and the bomb planters as poorly educated men from modest or deprived homes.
For example, Muktar Said Ibrahim and Yasin Hassan Omar, two of the 21 July suspects, were both from powerless migrant communities. Omar was placed in foster care and Ibrahim fell in with a street gang.
Whatever their social backgrounds, both groups are united by a deep-seated sense of injustice. This would have stemmed from social deprivation, some form of trauma, by images or first-hand experience of Muslims being ill-treated while the West stood by doing nothing. For this tiny minority, these feelings would have become twisted into something deadly when they attend trainingcamps.
Peter Herbert, a leading barrister, spent many hours interviewing Richard Reid, the Briton jailed for attempting to blow up a plane using bombs hidden in his shoes.
His impression was that Reid was very normal.
"His view of world politics was no different from people who turn to extremism," said Mr Herbert, chair of the Society of Black Lawyers.
He regretted any loss of life and said there was no personal hatred towards individuals. People justify killing by their greater agenda."