Image copyright Other

Many struggle to imagine what goes on in the minds of an Islamic State recruit. Nina Arif struck up a correspondence with one volunteer to try to find out.

It had been months since I'd heard anything from Muthenna Abu Taubah.

He was a fellow British Muslim who, like me, went to school in central London. Like me, he loved martial arts. Unlike me, he went to Syria and joined Isis.

Muthenna Abu Taubah was the alias of a man whose real name I never knew, but to whom I spoke for several months. He was a 24-year-old half-Irish, half-Nigerian convert to Islam. When I spoke last week to someone who knew him out in Syria I found out he was dead, killed in an accident in a bomb-making factory in Raqqa, capital of the so-called Islamic State.

I first came across Taubah in late 2014, after exhausting my contacts and spending hours trawling through social media. I approached the convert of four years as a Muslim journalist who wanted to provide an alternative to the dominant narrative on Isis fighters.

He agreed to answer my questions and we ended up communicating - by WhatsApp message - over a period of almost six months.

At first, Taubah spoke formally and stayed in character as a jihadi warrior. He directed me to his Twitter account where he'd gained quite a following by posting statuses about life in Syria, photographs of himself posing with his AK-47 and offering advice to other would-be jihadis.

Taubah had "signed a contract in blood" to help the Syrian people. It was their plight and that of other suffering Muslims, he said, which motivated him to join the group.

Image copyright Other Image caption Abu Taubah took pictures of his cat and of the food he liked

"Look at China - men aren't allowed to grow beards and Muslims aren't allowed to fast. Look at France - women can't wear niqab. Look at the USA and UK - you can't even talk about jihad." While I privately dismissed the links to propaganda he began to send me, which simplistically divided the world into good and evil, I could certainly empathise with grievances about Muslims having their freedoms curbed. I could agree too, that many innocent Muslims were paying the price in conflicts abroad.

But why had Taubah (Arabic for "repentance") chosen the path of jihad as a response to injustice? And weren't Isis committing injustices too? Soon I would question him about this. But first, I wanted to know about his past.

Half in jest, I probed him based on what I knew about the profiles of some jihadis: "Let me guess… in your pre-Islam life, you were in a gang of some sort, took drugs and went to jail?" He replied with "no comment".

He was only prepared to reveal that his past was "bad" and that he looked on the bright side now: "When life gives you lemons, you make lemonade."

Taubah gradually began to open up more, telling me he went to university in the UK, enjoyed Muay Thai, playing chess and once had a dog. He said his family didn't understand him, but he loved them and missed them - the Nigerian side (he never knew the Irish side).

In Syria, he cooked meals with his friends, adopted a cat and liked the "halal partying" on Eid, which meant "eating food and having fun with the ikhwan [brothers]". Taubah even learned to speak Arabic by mixing with the other fighters. He told me there were many foreign fighters living with their families in Raqqa, where it was "easier not to sin".

Despite his online persona, I wasn't sure if Taubah actually engaged in combat. When I asked what job he did for Isis, he vaguely told me: "We work for Allah in the day and rest at night." He said he couldn't reveal details for security reasons, nor did he want to jeopardise his family in any way. But I wondered if his withholding information might also have been because he planned to return home.

As well as bombarding me with jihadi literature, Taubah also asked questions like "how many countries have you travelled to?" and "what's the most horrific thing you've seen?"

He was sizing me up against himself to prove how much life experience he had despite being younger than me. "I've definitely got more life experience than you," he said.

It was almost 3am and I was struggling to stay awake but Taubah wanted to learn more about me. "One more question…" He wanted to know if I studied Islam, which scholars I listened to and what I thought about Isis.

I responded with: "I don't know, that's why I'm speaking to you." He soon asked: "What do you think of me?" I answered as blandly as possible, saying I thought he was passionate about his cause. "Is that it? Nothing bad? I think you're not being honest."

He was right. So I gave him a more honest answer: "Some of the things you've said to me… it's not a balanced way of looking at the world. I'm worried you'll do things you regret. You're very young and inevitably you'll change, and so will the way you view the world. The Koran says think, reflect and question things. I think you only see black and white."

This was the first time I sensed Taubah was annoyed that the barrage of jihadi propaganda he provided hadn't penetrated my mind.

After telling me I should learn my religion, he launched into a rant about Muslims in the West: "They don't value the mujahedeen. Instead they slander them and say they are harsh. But they would never say anything about the kuffar [non-believers]. They love living under kuffar laws…"

I soon received an abrupt message: "I have to tell you something. We should not be speaking anymore." And with an apology for saying anything "inappropriate", Taubah ended our conversation.

I respected his wish not to communicate, but just for four days. My gut feeling was that he wanted to speak, but was instructed not to (perhaps my scepticism towards Isis had made me less trust-worthy). I reopened our conversation by asking Taubah why he changed his mind and, for the first time, sensed doubt. "I have faults, I wouldn't be the best person to represent IS," he said.

But despite this, he continued to send me links to jihadi websites. "Some more propaganda for you. I'm trying to radicalise you if you didn't notice… I know you think I'm a terrorist."

This time, I decided to also send him articles with arguments by Muslim academics and scholars who opposed Isis. "I'm also trying to de-radicalise you."

But Taubah dismissed all the Muslims I'd cited as "kafirs" [unbelievers] and often grew tired of my non-acceptance of his world view. "There's no benefit in talking to you. I hate these conversations… I feel sorry for the man that has to put up with you." He frequently attacked me yet continued to communicate.

Taubah sent me a photo showing the leader of the Nigerian militant group Boko Haram pledging allegiance to Isis. "Do you agree with what they do?" I asked in reference to the kidnapping of schoolgirls.

"It is ok to kidnap the women from the kuffar as long as we don't have a treaty with them."

"Islam allows for young girls who are innocent to be kidnapped and sold? Seriously?? That could be your sister."

"Don't let your naffs [personal feeling] corrupt your views"

"You're the one who has non-Muslims in your family… So, tell me honestly, if IS wanted to kidnap and sell your non-Muslim relatives into prostitution, you wouldn't object to it?"

"You call the sunnah [teachings of the Prophet Muhammad] prostitution. Fear Allah."

Taubah was angry and when I asked for the evidence from scripture which sanctioned people-trafficking, he told me that I should look for it myself and learn my religion. "I'm tired of arguing."

By now Taubah's Twitter account had been shut down and he seemed worried when I told him that I had found an article about him online. I didn't understand why he was so worried and pointed out to him that he should have expected it, since he'd been very openly pro-Isis on his very public Twitter account.

He didn't agree: "It wasn't clear that I am IS, maybe a supporter." Taubah became standoffish, saying things like "are you intel?" and "I have you figured out… the conclusion isn't good".

Our exchanges became less coherent since Taubah became unwilling to continue debating. Instead he conceded: "We see the world differently because we have different understandings of the deen [religion]." Soon I stopped hearing from him.

Months passed and I often found myself wondering what happened to Taubah. I finally managed to reach somebody who knew him and I asked the first question that came to my mind, "Is Abu Taubah still alive?"

He was dead. He had been killed alongside his best friend in a bomb-making factory in Raqqa. I was told that the 24-year-old was engaged to be married when the accident happened. But he had once said: "Death is written for you. When it comes, you can't avoid it."

Aside from a lesson in scripted jihadi responses, our exchanges brought me insight into an individual who perhaps lacked the absolute conviction he first tried to project. It left me wondering how many others in the seemingly impenetrable Isis army could also be having doubts.

More from BBC News

At least 700 people from the UK have travelled to support or fight for jihadist organisations in Syria and Iraq, British police say. This BBC News database details the stories of those who have died, been convicted of offences relating to the conflict or are still in the region.

Who are Britain's jihadists?

Subscribe to the BBC News Magazine's email newsletter to get articles sent to your inbox.