Islamic State leader Abu Bakr al-Baghdadi in his first public appearance in Mosul, Iraq, in July 2014 (left) and in a video released Monday that purported to show him speaking to supporters.

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Islamic State leader Abu Bakr al-Baghdadi in his first public appearance in Mosul, Iraq, in July 2014 (left) and in a video released Monday that purported to show him speaking to supporters.