Even though the third American beheaded by the Islamic State in Iraq and Syria (ISIS) had converted to the Islam faith, the extremist organization nevertheless decapitated the 26-year-old former soldier who was known eventually as Abdul-Rahman Kassig.

Like the most recent beheading victims of the ISIS who were aid workers, Kassig first went to the Middle East as an American soldier and came back to provide medical assistance to war victims in the region. He was involved in aid work for one year in Syria when he was abducted by the militants.

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U.S. President Barack Obama, outraged by the death of a third U.S. citizen by decapitation after James Foley and Steven Sutton, was quoted by CNN as saying that Kassig "was taken from us in an act of pure evil by a terrorist group that the world associates with inhumanity."

Kassig, in an email from Beirut to his family on March 18, 2012, wrote that he discovered his calling in life in that land. He described his old life as "a selfish life."

He had also written to friends and former professors. After his capture, he was able to send a letter to his parents in which Kassig described his experience as "the hardest thing a man can go through," citing the stress and incredible fear he felt.

Kassig admitted to being scared of dying, but pointed out, quoted by BBC, "the hardest part is not knowing, wondering, hoping, and wondering if I should even hope at all."

His parents, Ed and Paula Kassig, in a statement, said they are heartbroken by their son's death while serving Syrian people. They also shared a previously unpublished audio statement Peter made and recorded by a journalist before their son was captured.

Obama condemned ISIS for reveling "in the slaughter of innocents," including fellow Muslims. The president said the extremist organization "is bent only on sowing death and destruction" and included Kassig as its victim, a humanitarian who was in the war-torn area "to save the lives of Syrians injured and dispossessed by the Syrian conflict."

TagsPeter Kassig, beheading, decapitation, ISIL, ISIS