It so happened that Senator John McCain had visited Ukraine on a official visit somewhere in the first week of June 2015. The hacktivists belonging to CyberBerkut somehow managed to access his laptop. This is what they had to say to Senator McCain,

According to the hackers, they broke into the laptop of one of the American politicians, Senator McCain and after found a video with staged IS execution, which they decided to show to the world community. From the video it can be seen that the entire set including the hostage is stage managed.  An actor dressed as an executioner of IS is holding a knife to behead the prisoner, and the “victim” depicts to be suffering. It may be recalled that IS have been repeatedly publishing the videos of the executions of hostages and if this video is true, the victims may in fact be alive. The authenticity of this video has not been independently verified.