Western intelligence sources tell NBC News that an admitted al-Qaida operative has told interrogators he took one of the London bombers to a terrorist training camp in Pakistan.
Monday, the Pakistan connection became indisputable, with solid evidence that three bombers visited there and that two met with al-Qaida operatives.
Photos show the leader of the bombers — Mohammed Sidique Khan — entering Pakistan last November, along with Shehzad Tanweer. Authorities say the two stayed in the country four months. Another bomber, Habib Hussein, also visited Pakistan.
U.S. sources say an al-Qaida operative now in U.S. custody, Mohammed Junad Babar, has told interrogators he took Sidique Khan to a suspected al-Qaida training camp in Pakistan during a previous visit.
"Al-Qaida was involved, at the very minimum, in the training — both in the ideology and combat skills required to conduct this operation," says retired Air Force Lt. Col. Rick Francona, an NBC terrorism analyst.
Pakistani authorities say that Tanweer also met with a different al-Qaida operative while in Pakistan and visited extremist Islamic schools.
Western intelligence sources say there's an "increasing sense" the London attacks were planned and directed in Pakistan. But were the attacks directed by al-Qaida? And if so, how high did the plot go?
"The intelligence community," explains NBC terrorism analyst Roger Cressey, "has believed for some time that any attack against the United Kingdom or the United States must be authorized by the al-Qaida leadership now in hiding."
British authorities acknowledge that the lead bomber — Sidique Khan — came up in a previous terror investigation and was deemed not a threat by British intelligence, so he was never even questioned.
Lisa Myers is NBC’s senior investigative correspondent