The man was identified as Haroon Rashid Aswat, 31, who was a senior aide to Abu Hamza al-Masri, the blind, one-armed militant cleric who preached violence in north London until his arrest in April 2004.
Scotland Yard suspects Aswat provided the four British bombers with support for the coordinated attacks in London's public transportation system, killing 52 people and wounding 700, intelligence officials told the New York Times.
The ethnic Pakistani Aswat's whereabouts are not known, but investigators said they were almost certain he was not in Britain now.
Aswat is believed to have met Osama bin Laden sometime in the late 1990s, and trained at al-Qaida-run camps in Afghanistan and Pakistan.
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