U.S. officials are working feverishly to decipher numbers and apparent codes in a notebook retrieved from suspected al Qaeda leader Abu Faraj al-Libbi, ABC News has learned. Al-Libbi -- believed to be third in command of al Qaeda leader after Osama bin Laden and Ayman al-Zawahiri -- was arrested by Pakistani authorities on Monday. He is suspected of leading two failed assassination attempts on the life of Pakistani President Pervez Musharraf. Sources said officials believe al-Libbi's seized notebook contains "hot" contact information. They said officials are hopeful the notebook contains useful information because al-Libbi was stunned when he was captured. One senior official described al-Libbi as "shocked" and enraged. "He thought he was invincible," the source said. "He was caught with his pants down. This was not the time and place of his choosing." Al-Libbi was trying to destroy the notebook when he was apprehended, multiple sources said.