ISIS has published another video allegedly showing the beheading of British hostage David Haines, 44, just hours after his family pleaded for his life. Stills from the video as well as links to it online began appearing on Twitter accounts associated with ISIS early Saturday evening. "Jihadi John," the masked killer who is believed to have also killed American journalists James Foley and Steven Sotloff in August, appears to be the murderer on video. Again, he called for an end to attacks against ISIS in Syria and Iraq by the United States and its allies, namely the United Kingdom. And as in other videos, he showed the likely next victim, identified as Alan Henning. The jihadist specifically warned British Prime Minister David Cameron to stop supporting the effort against ISIS. Cameron is expected to seek Parliamentary approval to join the United States in air strikes against ISIS positions in Iraq. Haines was a humanitarian aid worker who had worked in the Balkans, Africa and the Middle East since 1999. He was taken hostage in March last year, but his identity was kept secret for 19 months to allow time for the family to work for his release. Haines has two daughters, ages four and 17, and lived in Croatia after marrying his second wife, Dragana Haines.