As the CT Blog Experts and others predicted after the 7/21 attacks (Steven Emerson here and here and Evan Kohlmann here), the unexploded backpacks appear to be leading to a swift investigation of the links between the 7/7 and 7/21 attackers. The July 24 Guardian reports that "Police now believe some of the men they are pursuing for last week's abortive attacks...attended a whitewater rafting trip at the same centre as two of the 7 July bombers, Mohammad Sidique Khan and Shehzad Tanweer. Evidence discovered in the rucksacks left behind by the failed bombers led police to three addresses in London. When investigators cross-referenced them with the electoral register they discovered names that tallied with those of individuals who attended the outdoor adventure course in Snowdonia last summer. Scotland Yard has confirmed the explosive used in the 21 July bomb attempts bore a similarity to that used in the earlier attacks."
UPDATE, 7/24: Third Arrest Made in Botched London Bombings - and "Analysts: Al-Qaeda behind attacks: London, Egypt blasts mirror group's tactics" - The back-to-back nature of the attacks in Egypt and London, as well as similarities in the methods used, suggests that al-Qaeda might have ordered both operations and is a clear sign Osama bin Laden and his deputies remain in control, according to counterterrorism analysts and government officials in Europe and the Middle East."
London Daily Mirror photo: "Mohammed Sidique Khan (middle right showing V-sign) and Aldgate bomber Shezad Tanweer (bottom right leaning forward)"