Mr Emwazi Snr was questioned along with one of his sons for most of the day on Sunday after being summoned by police.
"The mother recognised the voice and she screamed 'that is my son' while he was talking before beheading the first American hostage," a source familiar with the Kuwaiti investigation said. "When they played the video again, the father was sure it was his son."
Insiders described Mr Emwazi as "emotional and upset at what had happened to his son" while talking to investigators.
"I am waiting day-by-day to hear about his death," he is said to have told his interrogators."
