The Islamic State has reportedly executed British volunteer aid worker Alan Henning, the fourth victim to appear in a execution video from the terrorist group since August. The video's authenticity remains unconfirmed, but the British Foreign Office released a statement that said, "if true, this is a further disgusting and senseless murder."

Henning's purported murder was revealed in a video released by ISIS just after 4 p.m. EST on Friday. The video, entitled “Another Message to America and Its Allies,” begins with a cable news segment discussing the United Kingdom’s role in air strikes against ISIS. British forces have been involved in reconnaissance missions over Iraq for weeks, but their first official airstrike on ISIS targets was Tuesday. Thursday, the United States released video of its own airstrikes on ISIS.

At the White House, President Obama's chief homeland security and counterterrorism adviser, Lisa Monaco, said administration officials were "evaluating" the latest video and that if authentic, it represented "yet another demonstration of the brutality of ISIL."

The release of the video on Friday evening coincides with the start of both Eid al-Adha, an Islamic holiday known as the Feast of the Sacrifice, and Yom Kippur, the Jewish Day of Atonement, which happened to fall on the same day this year.

Unlike the other ISIS beheading videos, Friday's video is only about a minute long (other videos were over three minutes) and the statements read by both the executioner and victim are quite short. Henning speaks only briefly, saying,

I am Alan Henning. Because of our parliament’s decision to attack the Islamic State, I as a member of the British public will now pay the price for that decision.

The executioner then speaks:

The blood of David Haines was on your hands, Cameron, Alan Henning will also be slaughtered but his blood is on the hands of the British parliament.

After the execution, another hostage appears, Peter Edward Kassig, an American and fellow aid worker. The executioner states:

Obama, you have started your air of bombardment in Sham, which keeps on striking our people so its only right that we continue to strike the next of your people.

Henning had appeared in ISIS's third execution video, of British journalist David Haines, which was released on September 13. (American journalists James Foley and Steven Sotloff were the first two victims to appear in execution videos.) Henning was on an aid mission in Syria, bringing supplies to a hospital, when he was taken hostage in December 2013. An avid volunteer, he has a tattoo on his arm which reads "Aid 4 Syria."

Alan Henning’s family and fellow volunteers called for his release when his life was first threatened. Prominent Islamic leaders in Britain and around the world have also pleaded his case, stating that Henning’s death would be in violation of Sharia law. However, other terrorist organizations have looked to the Koran to justify beheadings in the name of Islam.

The executioner in the video appears to be the same man from the previous three videos; however, his voice has been heavily manipulated. The voice also seemed to be manipulated in the David Haines video. Last week, the FBI confirmed it had identified the executioner, but did not release his name. He is known only as "Jihadi John" to the public. A former hostage said John is "intelligent, educated and a devout believer in radical Islamic teachings."

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