Zawahiri who turns 60 next month, helped found al Qaeda with bin Laden, merging bin Laden's group with his own Egyptian Islamic Jihad.
Together they issued a fatwa in 1998, believed to have been authored by Zawahiri, called "World Islamic Front Against Jews and Crusaders," and also called a general meeting of al Qaeda.
Their shared career of terror began with the U.S. Embassy bombings in Kenya and Tanzania later that year, and continued with the USS Cole attack of 2000 and then 9/11. Zawahiri is under indictment in the U.S. for the embassy attacks.
In April 2009, the U.S. State Department said that it believed that bin Laden had become a spiritual figurehead within al Qaeda, and that Zawahiri, known as "The Doctor" or "The Teacher," was the group's true operational and strategic leader.
Examination of the materials found in Bin Laden's Abbottabad hideout will show whether U.S. officials had it right.
A senior Pakistani official told ABC News Wednesday that Pakistan's intelligence agency, ISI, continues to believe that bin Laden had not been operationally involved with al Qaeda for some time.
Zawarhiri is still thought to be hiding near the Afghan-Pakistan border. (ANI)