In an interview with The Times, Mr. Ali agreed to listen to an audio recording of the recently captured Mr. Khalifa. “That’s him,” he exclaimed. Mr. Ali said Mr. Khalifa’s identity as the narrator was not widely known in the caliphate. “That’s not something he shares,” Mr. Ali said. “But once you speak to him, it’s obvious.”

In a two-minute televised statement after being captured by the Syrian Democratic Forces, Mr. Khalifa identified himself as an ISIS fighter and gave his name as Mohammed Abdullah Mohammed, which follows the Arab naming convention of his first name followed by his father’s and grandfather’s names. He admitted to attacking the local Kurdish militia but made no mention of his role as the narrator.

The brief statement was enough for analysts to recognize the voice as that of the narrator, though officials with the militia group said Mr. Khalifa initially denied his role.

In the interview with The Times, Mr. Khalifa spoke in the presence of two Kurdish prison officials, who recorded the exchange but did not interfere. He clarified that his legal name was Mohammed Khalifa, a detail confirmed by Mr. Amarasingam, who has been in touch with one of his childhood friends in Canada. Mr. Khalifa played down his significance in the Islamic State and insisted that he had not appeared in any execution videos beyond providing the voice-over narration, a claim that could not be immediately verified since most executioners wore masks.

He said he was born in Jeddah, Saudi Arabia, to parents of Ethiopian descent, earned a diploma in computer systems technology from Seneca College in Toronto and led an unremarkable work life as an information technology specialist, including for Kelly Services, an IBM contractor. IBM did not immediately respond to a request for comment.

Reached by phone, Kelly Services confirmed that a Mohammed Khalifa was contracted by the company from May 2009 to April 2010 in Markham, Ontario. Seneca College declined to comment.