Peter Kassig first visited Beirut on a college spring break trip. What the former Army Ranger from Indiana saw there prompted him to return, the next time as a medical assistant and humanitarian worker hoping to offer blankets, food and medical care to victims of the region’s conflicts.

Kassig founded a nongovernmental organization that provided aid for refugees fleeing the civil war in neighboring Syria. But his work in Lebanon led to his capture by militants on Oct. 1, 2013, while en route to eastern Syria.

On Friday, Kassig, 26, appeared in an online video that purported to show a masked militant who threatened to behead the Army veteran next, after the apparent beheading of British hostage Alan Henning.