Kayla Mueller, a humanitarian aid volunteer from Arizona, was captured in Syria and held hostage by ISIS and its leader, al-Baghdadi. Her death was confirmed in February 2015.
Al-Baghdadi was confirmed dead after he reportedly blew himself up with a suicide vest during a raid by U.S. forces this weekend.
Other Americans were among a rash of beheadings by the Islamic extremist terrorist group around the time of Mueller's death. They include another aid worker named Peter Kassig and journalists James Foley and Steven Sotloff.
Mueller wrote the below letter to her family while she was held prisoner.