United States officials implicated Zarqawi in over 700 killings in Iraq during the invasion , mostly from bombings . Since March 2004 , that number rose into the thousands . According to the United States State Department , Zarqawi was responsible for the Canal Hotel bombing of the United Nations Headquarters in Iraq on August 19 , 2003 . This attack killed twenty-two people , including the United Nations secretary general 's special Iraqi envoy Sergio Vieira de Mello . Zarqawi 's biggest alleged atrocities in Iraq included the attacks on the Shia shrines in Karbala and Baghdad in March 2004 , which killed over 180 people , and the car bomb attacks in Najaf and Karbala in December 2004 , which claimed over 60 lives . Zarqawi is believed by the former Coalition Provisional Authority in Iraq to have written an intercepted letter to the al-Qaeda leadership in February 2004 on the progress of the " Iraqi jihad " . However , al-Qaeda denied they had written the letter . The U.S. military believes Zarqawi organized the February 2006 attack on the Al Askari Mosque in Samarra , in an attempt to trigger sectarian violence between Sunnis and Shi'ites in Iraq
Canal Hotel bombing
Canal Hotel bombing
Abu Musab al-Zarqawi