In May 2009, the London-based human rights group Cage UK received a panicked phone call from a young man who had just been interrogated by the British security agency MI5. He had just returned from a trip to Tanzania when he was accosted by an MI5 agent who accused him of seeking to travel to Somalia to fight with Al-Shabab, a radical Islamist group waging a civil war against the country’s Western-backed government.

“He asked me, What do you think of 7/7?" the young man recalled, referring to the coordinated suicide bombing attacks that struck London on July 7, 2005. “I said, man, innocent people have died. You know, this is extremism!”

Next, the MI5 agent asked for his opinion of the US invasion of Afghanistan. The man replied that he opposed it on the grounds that innocent people were killed. It was a common view not only among British Muslims, but among supporters of the UK’s Labor Party in general.

“Then he starts telling me, What did you think of 9/11?" the man continued, with anguish rising in his voice. “I told him, this is a wrong thing. What happened was wrong! What do you want me to say? If I had the opportunity to make those lives come back, I would make those lives come back. I think what happened was wrong!”

This month, the exasperated young man heard in those phone calls was exposed by the Washington Post as the masked ISIS executioner known as “Jihadi John.” Back in May 2009, he was a 21-year-old University of Westminster graduate from West London named Mohammed Emwazi. Over the course of the next four years, the MI5 hounded Emwazi, attempting to recruit him as a spy and threatening him with harsh punishment if he refused to collaborate. By the time Emwazi left the UK in 2013, he had blamed the security services for driving him to the brink of madness. He would emerge soon after as the world's most notorious terrorist.

Asim Qureshi, a spokesman for CAGE who was approached by Emwazi in 2009 and documented his accounts of security service harassment, believes MI5 played a critical role in driving Emwazi into the hands of ISIS. “We have created here in the UK an environment in which the security agencies can act with impunity, can destroy the lives of young people, without any recourse to challenge them in an effective way,” Qureshi declared at a February 26 press conference in London where CAGE released its record of communications with Emwazi.

Five days later at CAGE’s office in West London, Qureshi explained to me, “We’ve never said it’s MI5 that’s solely responsible for his descent into violence. But MI5’s role is a contributing factor in making him want to leave the UK for Syria.”

“Why don’t you come work for us?”

Emwazi first appeared on the radar of the British security services when he embarked on a trip with a group of college friends to Tanzania in May 2009. The MI5 believed that Emwazi was on his way to joining Al-Shabab in Somalia at the time, even though he had landed in a country that did not share a border with it. Emwazi insisted he was planning a safari in Tanzania and even produced a return ticket to substantiate his claim.

He had managed to fly out of the UK without incident and was able to pass through Amsterdam, where he had spent two days, all while he and his friends were under careful MI5 surveillance. As soon as he arrived in Tanzania, Emwazi was detained by local authorities acting on directions from the MI5, then stripped to his underwear and held in a dark, mosquito-infested cell. Over the next 24 hours, he said strange men with guns periodically entered to cell to threaten him. Tanzanian authorities ultimately found nothing to prove Emwazi had plans to join Al-Shabab and deported him on the curious grounds of having exhibited drunken, belligerent behavior on the flight from Amsterdam.

When he returned to Amsterdam from Tanzania, Emwazi was greeted at the airport by an MI5 agent calling himself Nick. “[Nick] said that at the end of the day they had been following us and watching us closely,” Emwazi told CAGE UK. “I told him that it was news to me and I had no idea about it. He knew everything about me; where I lived, what I did, the people I hanged around with.”

Emwazi said Nick attempted to induce him into spying for the MI5: “Listen Mohammed: You’ve got the whole world in front of you; you’re 21 years old; you just finished uni —why don’t you work for us?”

Emwazi was adamant in his refusal, triggering an ominous warning from Nick: “You’re going to have a lot of trouble… You’re going to be known… you’re going to be followed… life will be harder for you.”

The MI5 had apparently attempted to blackmail Emwazi, offering him an escape from its ever-tightening dragnet on the condition that he spy for them. Though the British government never formally charged Emwazi with any offense, the MI5 interrogated his fiancee and her family in Kuwait, and gradually stripped him of his ability to travel or work outside the UK.