Alan Henning, a 47-year-old Briton who volunteered to help drive an aid convoy to Syria for Muslim charity Aid4Syria, was kidnapped 10 months ago.
"An audio file of Alan pleading for his life has just been received by me," his wife Barbara said in a statement released yesterday through Britain's Foreign Office.
"He went to Syria to help his Muslim friends deliver much needed aid."
"We are at a loss why those leading Islamic State cannot open their hearts and minds to the facts surrounding Alan's imprisonment and why they continue to threaten his life."
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Barbara Henning said that her attempts to communicate with the IS group had been ignored, and that she had learned that Henning had been cleared by an Islamic law court.
"I have been told that he has been to a Sharia Court and found innocent of being a spy and declared to be no threat," she said.
"I implore Islamic State to abide by the decisions of their own justice system. Please release Alan."