The 7/7 coroner has sharply criticised MI5 as she ruled that the emergency services could not have saved any of those who died in the attacks.
Lady Justice Hallett said the 52 victims of the July 2005 London bombings were unlawfully killed by four Muslim extremists and rejected claims that security agency failings caused or contributed to their deaths.
But she raised serious concerns about how MI5, also known as the Security Service, investigates and prioritises suspects, warning that poor record-keeping could allow flawed decisions to slip through with "dire consequences".
Lady Justice Hallett made nine recommendations for the Security Service, the emergency services and Transport for London aimed at preventing other deaths in the future.
She singled out MI5's "dreadful" editing of a sharp colour photograph of 7/7 ringleader Mohammed Sidique Khan and his number two Shehzad Tanweer, taken by an undercover surveillance team at a motorway service station in February 2004.
At this time the Security Service did not know who the pair were, although they had been seen meeting a known terrorist who was plotting a fertiliser bomb atrocity.
The cropped blurry black-and-white image of Khan was meant to be shown to al Qaida supergrass Mohammed Junaid Babar, who met the British jihadist at a terrorist training camp in Pakistan. But the picture was never put before Babar, apparently because its quality was so poor.
The coroner also highlighted the bereaved families' concerns about the limited records kept by MI5 about decisions on prioritising suspects and warned of the "possibly dire consequences of a flawed decision which cannot be properly supervised".
Lady Justice Hallett recommended that MI5 should examine its procedures "to establish if there is room for further improvement in the recording of decisions relating to the assessment of targets".
The bombings carried out by Khan, 30, Tanweer, 22, Hasib Hussain, 18, and Jermaine Lindsay, 19, were the worst single terrorist atrocity on British soil.