The ISIS militant who became known as "Jihadi John" was "well-mannered and "never lost his temper," a former co-worker told NBC News Monday. Mohammed Emwazi, who was unmasked Thursday as the person holding a knife to the neck of captives in the terror group's beheading videos, was a model employee at the Kuwaiti tech company where he worked as salesman in 2010. “He was very committed, disciplined," the former colleague said. “He never lost his temper or showed any violent tendencies." Emwazi is directly linked to the killing of at least four Western hostages, including American journalists James Foley and Steven Sotloff.