ISIS has beheaded British aid worker David Haines. The video features the terrorist known as Jihadi John, and includes a threat to kill another British hostage, .\r<br>\r<br>Warning: This video may be disturbing. After showing a clip of British Prime Minister David Cameron, ISIS releases A Message to the Allies of America, which .\r<br>\r<br>\r<br>\r<br>ISIS has beheaded British aid worker David Haines. The video features the terrorist known as Jihadi John, and includes a threat to kill another British hostage, .\r<br>\r<br>Warning: This video may be disturbing. After showing a clip of British Prime Minister David Cameron, ISIS releases Another Message to America and Its Allies, .\r<br>\r<br>
