BAGHDAD — The Iraqi authorities released a video on Friday with the confession of a recently captured Islamic State operative who was involved in a notorious incident in which captured Kurdish soldiers were put in cages and paraded around a northern Iraqi city by hooded Islamic State fighters.

At the time, early 2015, the Islamic State was threatening to burn them to death much as they had done two months earlier to a Jordanian pilot who had been captured, caged and then set on fire in Syria. It is not clear how the Kurdish captives were killed.

The captured operative, Jamal al-Mashadani, who was known by the nom de guerre Abu Hamza al-Kurdi, was an officer in President Saddam Hussein’s security apparatus before joining Al Qaeda in Iraq after Mr. Hussein’s fall. Mr. Mashadani later shifted his loyalty to the Islamic State.

He is one of a relatively small number of midlevel and higher level officials to have been captured by the Iraqis, the Americans or through the combined efforts of American and Iraqi intelligence services. Five other Islamic State officials were captured in May. The Iraqis have also captured several thousand lower-level fighters. Many other Islamic State officials and fighters were killed in battle.