Was Mohammed Emwazi, the man with a British accent who's appeared in numerous ISIS beheading videos, pushed toward extremism by authorities? Or was he someone who'd long been heading down a militant path?
But some analysts say the emails are only part of the story, arguing that investigators targeted Emwazi because they already saw he had links with terrorist groups.
"You can't start the story at how he's been treated by UK officials. You certainly can't start the story from the email trail," said Rashad Ali, director at the counterextremism consultancy CENTRI and a fellow of the Institute of Strategic Dialogue. "You have to go back to why the intelligence services got in contact with him. Well, because he was part of a group of a people who were going to join Al-Shabaab -- a very extremist organization and jihadist group that got involved in horrific terrorist attacks in Somalia."
Pleading for help
Emwazi felt he was being harassed by authorities and tried to seek legal help to stop it, according to CAGE, the human rights and Muslim advocacy organization that worked with him.
One email details Emwazi's account of his detention at a British airport, when authorities stopped him from traveling to Kuwait in 2010 and questioned him for hours.
"I told them that I want to be left alone, as I have an ambition of moving from the UK and settling in Kuwait. That is why I found a job and a spouse!! But they laughed," Emwazi wrote in a message dated June 3, 2010.
"One of them got aggressive with me, he pushed me to the wall. ... I was just baffled I did not know why he had done that after this long 6hour interview, fingerprinting and searching. When I asked for their names they said 'We don't give out our names.' "
Emwazi wrote that the way he was treated by British security and intelligence officials reminded him "of criminals that you see on TV who have committed a serious crime, only I was a person never charged or arrested for anything. I was a person looking to start a new life in my country Kuwait!"
That's a key detail, CAGE spokesman Amandla Thomas-Johnson said.
"If someone is going to carry out some violent attack in any kind of way, then the law is there to be in force and apprehend them," he said. "In the UK, he wasn't arrested once, prosecuted or cautioned whatsoever."
British authorities have not responded to CNN's requests for comment on the case.
In the emails, Emwazi pleaded for CAGE's help.
"Please help me as I don't want to stay in the UK because I have found a Job in Kuwait, found a spouse in Kuwait and thus found a new start for my life in Kuwait. Kuwait is where I'm from, I was born their. I just want to go their and start my new life again!!"
Emwazi wrote that he had also made a formal complaint at the Independent Police Complaints Commission, before going into detail about how he was apparently "assaulted by the police officer" as he attempted to leave for Kuwait.
But it was a difficult complaint to prove, Thomas-Johnson said.
"The IPCC says there's no camera in the room where this took place, so we can't really do much about it except put a black mark against the officer," he said. "These things happen in the shadows and the dark. So it is very difficult to independently verify once it's taken place. There isn't much of an opportunity to gain redress and accountability."
Analysts: Harassment alone doesn't breed terrorism
Details from court papers reported in British media paint a different picture. They say Emwazi was part of a group of extremists sometimes called the "North London Boys" who allegedly funneled money and recruits to Al-Shabaab.
The Guardian has reported
that Emwazi was part of a terror cell with links to the failed London bomb attacks in 2005. To British authorities, his face was a familiar one for more than five years.
But authorities lost track of him in 2013, according to friends. He changed his name and made his way to Syria.
Analysts who've studied ISIS recruiting say they aren't buying the argument that harassment from authorities turned Emwazi into "Jihadi John."
"I think it's an absurd claim," said Peter Neumann, director of the International Centre for the Study of Radicalisation. "It was not the cause of his radicalization. The reason the intelligence services harassed him was because they suspected him of trying to join the Shabaab in Somalia."
Ali argued that abuse at the hands of officials is not an excuse for terrorism.
"People do not turn around, when harassed and have grievances, and become terrorists," he said.
Editor: Emails to newspaper show 'warped sense of injustice'
In addition to the emails released by CAGE, another series of emails from Emwazi came to light over the weekend. The messages were sent in 2010 and 2011 to the Daily Mail's security editor, Robert Verkaik.
The Daily Mail published excerpts from those exchanges, including Emwazi's description of an incident where he tried to sell his laptop through a website, but only stated his surname.
When he met a potential buyer at a London underground station, he says the person he met shook his hand and said "nice doing business with you Mohammed."
"I NEVER TOLD THIS PERSON MY FIRST NAME!!" wrote Emwazi to Verkaik. "& I NEVER GIVE OUT MY FIRST NAME!! IT WAS IMPOSSIBLE FOR HIM TO KNOW MY FIRST NAME!!"
He also hinted at suicidal thoughts. "Sometimes i feel like im a dead man walking, not fearing they may kill me.
"Rather, fearing that one day, I'll take as many pills as I can so that I can sleep for ever!! I just want to get away from these people!!!"
Verkaik said he met Emwazi in 2010 when he was investigating his claims of being harassed by police and intelligence.
Emwazi's concerns bordered on paranoia, Verkaik wrote, and he desperately wanted his story to be told.
"Like many young Muslim men at the time, he appeared to have a grievance. But this man was different," Verkaik wrote. "In him was a warped sense of injustice that could never justify the barbaric acts of murder that he has gone on to carry out in Syria."