A large cache of audio tapes left behind at Osama bin Laden’s headquarters in Kandahar, Afghanistan, in 2001 was released Wednesday, offering a portrait of his gradual transformation from Saudi militant to global threat and opening a window on the daily lives of men recruited for jihad.

While Mr. bin Laden’s evolution from opposing Saudi Arabia’s ruling dynasty to running an international terrorist organization has been detailed before, said Flagg Miller, an assistant professor at the University of California, Davis, who spent five years translating the tapes, the recordings provide a more spontaneous look at Al Qaeda than what is available through the carefully choreographed messages it releases.

“These are back-room conversations of Al Qaeda’s key operatives as well as fresh or potential recruits who are trying to figure out what the heck is going on and what their role in it is,” Mr. Miller said.