The alleged ringleader of the July 7 London bombers was tracked by intelligence services last year, the BBC has reported.
The investigation suggested that he was in contact with activists from Al Qaeda, Osama bin Laden's global terror network for five years before the blasts which killed 52 commuters and the four bombers themselves.
He featured in a surveillance operation by intelligence services, the investigation, aired on radio and television Tuesday, said.
The terror suspect he was talking to could not be named for legal reasons, the BBC said.
The Metropolitan Police identified Khan, a British Muslim of Pakistani origin, as one of the four men who blew up three Underground trains and a double-decker bus.
The teaching assistant was linked to the bomb in an Underground train near Edgware Road station which killed seven.
Khan hailed from Dewsbury, south of Leeds in northern England.
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