American hostage Kayla Mueller was murdered by the so-called Islamic State, and not killed in a coalition airstrike as IS claims.

That is the testimony of a Yazidi woman who escaped after being held as a sex slave, one of thousands of women and girls enslaved by IS.

Two Yazidi eyewitnesses have also told the BBC that Kayla was used by the IS leader himself as one of his personal sex slaves.

The BBC's Paul Wood and cameraman Fred Scott report from northern Iraq.

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