Daybreak's Lucy Watson speaks to Debra Accomondo - who knew one of the victims of the US shooting.
She told Daybreak: "It's one of those defining moments where you know your world is going to change."
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Some 66 people have been killed after the plane they were travelling on crashed in southern Iran.
The letter calls for an end to harassment, abuse, and impunity in a world "ripe for change".
Police say that anyone who sees Whitehouse should not approach him, but instead call them on 999 and quote incident 23 of 18 February.