The mother of Mohammed Emwazi has said she immediately recognised his voice when she heard him on a hostage video released by Islamic State.
The parents of Emwazi, 26, told Kuwaiti authorities they were last in contact with their son in 2013 when he called them from Turkey.
They said he told them he was going to do humanitarian work in Syria.
Meanwhile the Department for Education is to investigate schools with links to pupils who have travelled to Syria.
Quintin Kynaston Academy in north-west London, where Emwazi had been a pupil, is to be investigated along with another six schools.
Emwazi, from west London, who is also known as “Jihadi John”, has been named as the man in several IS videos where hostages have been beheaded.
He first appeared in a video last August, when he apparently killed the US journalist James Foley.
Intelligence officials in Kuwait are believed to have questioned his mother and father in the past day.
Authorities are investigating what Emwazi did, where he went and who he met there during his 2010 visit.
Emwazi’s father said his son was a devout Muslim from a young age, and the last contact he had had with him was in the middle of 2013 from Turkey – when he contacted the family to tell them he was going to join a charity in Syria.
Kuwaiti officials have described Mohammed Emwazi as being “an illegal resident” when he lived in Kuwait.
They confirmed to the BBC that he had never held Kuwaiti nationality nor held any Kuwaiti documentation such as medical or educational certificates.
Although Emwazi was born in Kuwait in August 1988, his family are from the so-called “Bidoon” or “stateless” community of southern Iraqi immigrants, many of whom were deported after Kuwait was liberated from Saddam Hussein’s forces in 1991. BBC
