ISIS Leader al-Baghdadi May Have Had U.S. Hostage Executed, Witness Says. Terrorism, United States Politics and Government, Kidnapping and Hostages, Murders, Attempted Murders and Homicides, Islamic State in Iraq and Syria (ISIS), Adnani, Abu Mohammed al-, Baghdadi, Abu Bakr al-, Mueller, Kayla (1988-2015), Sayyaf, Abu (d 2015), Syria, Sayyaf, Umm