The Denver shuttle bus driver at the centre of a federal terrorism investigation has begun to cooperate with the authorities, admitting that he had perhaps unwittingly crossed paths in Pakistan with extremists allied with al-Qaeda, said government officials.

The officials did not indicate whether the admissions of the man, Najibullah Zazi, made during three days of intense questioning by FBI agents in Denver, clarified whether he had directly engaged in terrorist activity. And it is not known whether he will be charged with any wrongdoing.

But Zazi’s discussions with the authorities shed light on the suspicions that led federal and New York counter-terrorism officials to begin intensive inquiries and to raid apartments in a suburb of Denver and in Queens, New York, believing he was the central figure in some kind of terrorist activity.

Zazi’s statements suggest a somewhat different narrative than the one he presented this week when he denied being affiliated with al-Qaeda and said he had no idea why the government would suspect him of wrongdoing. Indeed, there are now some indications that Zazi received training in explosives and bomb-making while overseas.