Mohammed Emwazi was "very good with people" and was "calm and decent", according to the head of an IT firm in Kuwait, which hired the then 21-year-old as a salesman.

He also expressed shock the person he had known was behind the reign of terror in the IS videos.

Emwazi, 26, is believed to have murdered at least five Western hostages, including British men Alan Henning and David Haines. His ex-boss told The Guardian newspaper: "He was the best employee we ever had.

"He was very good with people. Calm and decent. He came to our door and gave us his CV."

The executive added: "How could someone as calm and quiet as him become like the man who we saw on the news? It’s just not logical that he could be this guy.

"Maybe he fell into the wrong hands when he went back."

Emwazi left the company suddenly in April 2010 after returning to London.

Further details about the killer came as emails emerged suggesting Emwazi considered suicide when he was a student, after suspecting MI5 was closing in on him.

He told a journalist in 2010 that he felt like a "dead man walking".

Emwazi had also contacted a campaign group after he was questioned by counter-terrorism officers while attempting to fly from Heathrow to his native Kuwait in 2010.

In emails to the CAGE organisation, he claimed the security services were "stopping him from living his new life" abroad, where he had secured a job and was getting married.

When Emwazi was first unmasked as "Jihadi John", representatives from CAGE described him as "extremely kind and gentle" and "the most humble young person we ever knew".

The high school Emwazi attended, Quintin Kynaston Academy, is being investigated by the Department for Education - after a Sunday Telegraph report claimed that two other pupils from the north London school had been killed fighting for al Qaeda and al Shabaab.