Mother recognised Mohammed Emwazi's voice on hostage videos
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.
Meanwhile the Department for Education (DfE) announced it would carry out a review of schools that had links with pupils who had travelled to Syria.
A DfE spokesman said it had set up the Due Diligence and Counter Extremism (DDCE) division to improve its understanding of extremism and help schools with pupils or former pupils who have since travelled to Syria or "other areas of concern".
It said the task force would consider "if there are any lessons we can learn for the future".
The announcement came as Home Secretary Theresa May defended her decision to scrap control orders after Labour suggested it had helped terror suspects join fighting overseas.
Shadow home secretary Yvette Cooper said the relocation powers contained in control orders should not have been ended.
Mrs May said she could not comment on individual cases and that control orders would not have stopped Britons travelling to Syria.
Earlier, a former head teacher of Emwazi denied he had been radicalised at school.
Two other pupils from the same school are also thought to have gone to fight in Syria and Somalia.
Jo Shuter, former head teacher at Quintin Kynaston Academy, said there had been no indication that any pupils were becoming radicalised.
She said: "I am not prepared to say when the radicalisation took place. All I can say is absolutely hand on heart, we had no knowledge of it. If we had we would have done something about it."