Many have denied that they were linked, but they may have been. From the TimesOnline, :
INVESTIGATORS are trying to establish the first definite link between the two teams of London bombers.
Since the second attacks on July 21, Scotland Yard has been trying to discover if alleged members of the two cells met.
There were reports from Pakistan yesterday that a terror suspect named as the alleged leader of the 21/7 group was in the country this year at the same time as two of the men killed in the suicide bombings on July 7.
Security sources in Islamabad are trying to establish whether Muktar Said-Ibrahim met two Yorkshire-born suicide bombers who were in the country at the same time.
Both Shehzad Tanweer and Mohammad Sidique Khan had family ties in Pakistan though relatives say they do not know where the pair stayed during their three-month trip this year. What interests police is where Mr Ibrahim visited, as the 27-year-old Eritrean refugee has no known family connections in Pakistan.
He is expected to be asked about his recent overseas travels during his continued questioning at Paddington Green high-security police station.
One senior security source said: “It could just be a coincidence or it could be a vital lead in establishing how these operations were planned, financed and executed.”…
Counter-terror officers are still checking whether the two groups attended the same radical mosques here and abroad.
There are reports that Khan, who lived in Dewsbury, West Yorkshire, was a frequent visitor to the Finsbury Park mosque in North London.
Mr Ibrahim and others suspects from the 21/7 cell lived close to that mosque and are reported to have worshipped there together.