osama bin laden
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Al Qaeda leader Ayman al-Zawahiri, who was on the FBI's most-wanted list, was killed by a CIA airstrike in Afghanistan over the weekend. Al-Zawahiri helped plan the Sept. 11 attacks and was Osama bin Laden's replacement as leader of the terrorist group. Bin Laden once said, 'Killing Americans is a duty for every Muslim.'
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Al-Zawahiri took over for Osama bin Laden as leader of Al-Qaeda in 2011.