Perspective: Robin Cook stated in the Guardian shortly before he died, "Al-Qaida, literally "the database", was originally the computer file of the thousands of mujahideen who were recruited and trained with help from the CIA to defeat the Russians." (guardian)
See government references to Al Qaeda in the reports analysis
Almost immediately after the bombings it was reported that a claim from the 'Secret Organisation Group of al-Qaeda in Europe' had been found on a website. See BBC: Full text
MSNBC: MSNBC TV translator Jacob Keryakes, who said that a copy of the message was later posted on a secular Web site, noted that the claim of responsibility contained an error in one of the Quranic verses it cited. That suggests that the claim may be phony, he said. "This is not something al-Qaida would do," he said.
Even though the group were not ever considered credible the mainstream reporting of the claim continued for several days and then the story vanished without conclusion.
Observer: A videotape of Mohammed Siddique Khan released after the attacks also featured footage of Osama bin Laden's deputy, Ayman al-Zawahiri. The Home Office believes the tape was edited after the suicide attacks and dismisses it as evidence of al-Qaeda's involvement in the attack.
The video of Khan is the strongest piece of evidence linking the men with Al Qaeda. People that knew Khan have commented on the video being faked. Past videos released through Al Jazeera have been widely regarded as fake. It is possible Khan was influenced by some form of hypnosis or that he partook in the video to maintain a cover story. No official verdict on the video has been made by the authorities. Unconfirmed security sources reported different opinions on where the film was recorded. see below
Several men related to Al Qaeda have confessed to recognising Khan. These statements may have been made under conditions of torture or through bribery relating to money or jail time. A 'thumb drive' with details of the bombings was apparently found on an 'Al Qaeda operative' in Iraq. As with the video of Khan none of these media reports have been confirmed or concluded by Scotland Yard. see below
Aswat was initially reported to have spoken to Khan and Tanweer via telephone prior to and actually on the 7th July. These reports abruptly stopped in Britain after it became clear that Aswat had been an MI6 asset. He was arrested in Zambia and flown back to the UK. Scotland yard have since played down any link between Aswat and the bombings. He is currently in a trial where the likely outcome will be his extradition to the USA for charges of conspiring to set up terrorist training camps. see mastermind section
Independent: Revealed: British bomber had links with al-Qa'ida
Pakistan Tribune: Pakistan dismisses involvement in 7/7 suicide bombings
BBC: Full transcript
Guardian: Friends claim Khan's statement was faked
Independent: Footage shows bombers not 'duped'
Telegraph: Al-Qa'eda claims responsibility for July 7
Guardian: Al-Qaeda 'link to 7/7' found in Iraq
Aswat phone calls