As Isis continues to dominate our collective consciousness, most recently with the crucifixion of a 17-year-old boy, the government appears to be fumbling in the dark for new ways of stemming the blood from an old wound which refuses to heal; only they seem to be thinking about bigger plasters, which probably won’t do the trick. Meanwhile, somewhere in the UK, another jihadist is born.

I documented the birth of one particular jihadist in my BBC3 film My Brother the Islamist. The film charted my attempts to reconnect with Rich, who happened to be my stepbrother, to try to understand the new world he had become a part of. Ultimately the shared journey drew us closer together, but a year later he would be arrested for attempting to join the Taliban in Pakistan.

Only two weeks before he vanished from the streets of Ealing (I haven’t spoken to or seen him since he was taken into custody), we met for a coffee. We talked about our family, football, and albeit fleetingly, the future. I left the meeting with a smile on my face. Six months later he would plead guilty to terrorism charges, and I began making a second film, My Brother the Terrorist.

From the moment he converted, Rich was talking about fighting western oppression and dying a martyr. In a sense, the writing was on the wall. Violent jihad was something he and his “brothers” constantly talked about. When Rich pleaded guilty to preparing to commit acts of terror in 2012, he had been planning to travel to Afghanistan to cross the border and join the Pakistani Taliban.

But I never saw Rich as a terrorist, and didn’t see any of the people he surrounded himself with as terrorists either. What I saw were, and I hate to say it – vulnerable young men – with massive great chips on their shoulders. With their radical new status they felt empowered, superior and perhaps most annoyingly for me, righteous.

In a former life, the world they had been brought up in had wronged them. Perhaps they had family troubles, or maybe society shunned them, whatever it was, they resented it – they were lost, empty and had no stake in the western world. Becoming a radical Muslim reversed the polarity.

It’s a cliquey club from which everything beyond is viewed as imperfect at best, or evil at worst. And it’s the evils that these guys saturate their perceptions of the world with. Horrific, graphic and brutal images of the suffering, pain and death of Muslims at the hands of the west, played out alongside a powerful narrative of oppression and injustice – a narrative that is difficult to dismantle.

The irony is that the very shock of seeing such graphic brutality, which plays such a key role in the radicalisation process, eventually becomes ordinary. The powerful human response to violence becomes nullified, and they become blind to the evil they themselves help to perpetrate.

People like my stepbrother justify fighting violent jihad out of a sense of responsibility and powerlessness at the plight of fellow Muslims. Yes, fighting on a foreign battlefield and owning your own AK-47 is pretty exciting too (and let’s not forget that dying a martyr is like hitting the afterlife jackpot), but crucially their motivation isn’t to kill innocent people, or to do bad. They’re not thinking about blowing themselves up at a tube station, the story they’re telling themselves is, as confounding as it sounds – one of saving humanity.

In hindsight, Rich’s arrest and subsequent conviction shouldn’t have come as a surprise to me: he set out to do what he had always talked of. As I stood in the public gallery and heard the evidence put forward by the prosecution, I looked into the dock to see Rich’s stony face (which would shortly afterwards utter the word “guilty”), and felt let down and sad, but also unexpectedly stupid. The proverbial wool had been pulled over my eyes – our last meeting at the coffee shop had filled me with hope and optimism, but Rich knew it was potentially our last. In retrospect, maybe I should have taken him more seriously.

The inherent problem in attempting to tackle radicalisation is that often it is too late. By the time its signs begin to show, the scene is already set. Extremism of any kind is a symptom of an unhealthy society and, like any illness, in order to eradicate it, we should look to treat its cause.

Yes, charismatic ideologues play a part in the radicalisation process. But deep down, for those who are vulnerable, it’s not really about religious conviction or saving the world from oppression or defeating the evil west – these are just emotional vents; justifications for appeasing the deep lonely spaces of the human condition. It’s about feeling important, valued and ultimately, having a stake in the world surrounding them.

• My Brother the Terrorist is on BBC1, Wednesday 22 October at 23:05