Peter Kassig first went to the Middle East as a U.S. soldier and returned as a medical worker, feeling compelled to help victims of war.

"We each get one life and that's it. We get one shot at this and we don't get any do-overs, and for me, it was time to put up or shut up," he said in a 2012 interview with CNN.

Now Kassig, 26, is being held hostage by ISIS.

His life was threatened Friday in an ISIS video that showed the apparent beheading of British aid worker Alan Henning.

In a statement Friday, Kassig's parents, Ed and Paula Kassig of Indianapolis confirmed that he was being held hostage by ISIS but provided no other details. They had maintained silence about his capture since he was taken hostage in 2013.

"The Kassig family extends our concern for the family of Alan Henning," Kassig's parents said. "We ask everyone around the world to pray for the Henning family, for our son, and for the release of all innocent people being held hostage in the Middle East and around the globe."

Kassig's journey began when he joined the U.S. Army Rangers in 2006 and deployed to Iraq in 2007. He was honorably discharged for medical reasons after a brief tour and returned to the United States to study political science and train for 1,500-meter races. But something wasn't right.

"I was going to school with kids who look the same, were the same age as me, but we weren't the same," he said. "I wanted more of a challenge, a sense of purpose."

In 2010, Kassig took time off and began his certification as an emergency medical technician.

In the two years that followed, he fell in love, got married and quickly divorced. Devastated and heartbroken, he went back to school, but he couldn't shake his depression.

"I needed a game changer," he said.

He decided he would head to Beirut, follow the situation in Syria and try to help. So, on his spring break this year he packed his medical kit and flew into the Lebanese capital.

The next two weeks were filled with eye-opening misadventures as Kassig began to scratch the surface of the complexities of the Syrian conflict and the Middle East as a whole.

(CNN)