In 2003, al-Shami joined al-Tawheed wal-Jihad leader Abu Musab al-Zarqawi in north-eastern Iraq. He was appointed to the advisory council of the group and soon became Zarqawi's second in command. He was both spiritual advisor to the group and directed many of its attacks and battles against American and Iraqi forces. In a letter he wrote that his 300 mujaheddin had fought-off over 2,000 U.S. Marines in the First Battle of Fallujah.Letter Signed by Omar Yousef, May 2004
