According to Fox News, his parents had also received a threat by IS extremists that their son would be beheaded.
The parents, Ed and Paula Kassig said in a statement that a former hostage had told them that their son Peter Kassig had voluntarily converted to Islam last year when he had shared a cell with a Syrian Muslim.
The letter by Peter Kassig also said that he was at peace with his conversion to Islam and thanked his parents for strength and commitment. He appeared as if he was preparing for death.
Kassig was taken into captivity on October 1, 2013 where he was working as an aid worker.