The U.S. has obtained a 13-page letter written by Osama bin Laden's deputy, Ayman al Zawahiri, to Abu Musab al Zarqawi in Iraq, outlining with what one senior official calls "chilling clarity" al Qaeda's stretagy for Iraq and beyond, reports CBS News national security correspondent David Martin. The letter, which was written shortly after the London bombings in July, calls Iraq "the place for the greatest battle of Islam in this era." Zarqawi is America's most-wanted insurgent in Iraq. Zawahiri, the man most intelligence analysts believe is the brains behind bin Laden and his al Qaeda terrorist organization, is considered...