Mark White, Sky News, May 4, 2016

Sixty-three of the jihadis listed in the thousands of IS files obtained by Sky News swapped lives in the UK for the battlefields of Syria and Iraq.

Half of those are from London–with some linked to Islamic State’s most shocking crimes.

Over a number of weeks, Sky News knocked on the door of every address in the capital that we linked to the files.

This provoked various reactions; some were shocked, some angry and some upset.

Many of the families claimed they had no idea why their loved one had turned their back on them and some had even risked their lives trying to get them back.

We also discovered some distinct themes; most who joined Islamic State were from immigrant or refugee backgrounds.

More surprisingly, perhaps, was that nearly all of the extremists we investigated were well-educated and gave up promising lives in the capital.

Ibrahim Kabir Sadiq comes from an Eritrean Christian family who fled the conflict there and, as refugees, resettled in North London.

Sadiq stunned his parents when he converted to Islam while studying Economics at Nottingham University.

In a video he made about his newfound faith, he said: “After converting to Islam, my family weren’t happy. They’re still not happy.”

Those closest to Sadiq told Sky News how he has tried to lure others to join him fighting in Syria.

A close friend said: “I’ve spoken to him while he was out there and he said to me ‘come over’. But, I don’t believe in the things he believes in.

“People come up to me to ask me why they haven’t seen him in such a long time. I sometimes dodge the question. It depends on who’s asking.

“If we are close I might tell them. If not, I make something up, like saying he’s a teacher and moved away.”

In Walthamstow, east London, a group of Catholic Portuguese immigrants moved to the capital to study. They became friends and, one-by-one, converted to Islam and joined IS.

The group’s ringleader, Nero Saraiva, joined the terror group in April 2012, and is now a senior figure in IS.

He is believed to have played a part in the executions of Western hostages.

Saraiva posted a message on Twitter a month before American hostage James Foley was beheaded, saying: “Message to America, the Islamic state is making a new movie. Thank u for the actors.”

One of Saraiva’s close friends in Walthamstow, Fabio Pocas, has also risen in the ranks of IS. The talented footballer played for amateur teams around East London before leaving for Syria a year after Saraiva.

And in West London, one family is still in shock after their son left with no warning.

Safio Halfaoui was brought up by Algerian immigrants in Hayes, where he studied IT.

His family told Sky News he showed no signs of extremism.

His father said his son went missing after claiming he was going to a job interview, but never returned.

Halfaoui’s father said: “He asked for a lift. I dropped him off and never saw him again.

“He didn’t even say goodbye. I went to Turkey two years ago. I travelled there to try and find him but I couldn’t. I was told it was too dangerous for me to keep looking.

“Anyone who joins Islamic State is stupid. He was just a normal kid. But now he has hurt this family. But he’s my son. I want him to come back.”

Halfaoui’s uncle also claims he was arrested and lost his job at Heathrow Airport as a result, adding: “He’s destroyed this family.”

There were, of course, too many stories to tell from Sky’s investigation. These are just a few.

The files offer a glimpse of just how many young men are turning their back on Britain in pursuit of Islamic State’s brutal ideology. And, indeed, how they may not be what would normally be expected.

What the files don’t show, however, is the trail of devastation left behind for their families.