13 September : UK humanitarian aid worker David Cawthorne Haines was purportedly beheaded in a video .
UK humanitarian aid worker David Cawthorne Haines 's life had been threatened by Mohammed Emwazi in the Steven Sotloff video .
13 September : UK humanitarian aid worker David Cawthorne Haines , whose life had been threatened by Mohammed Emwazi in the Steven Sotloff video , was purportedly beheaded in a video .