We’re a little late with this, but the story went online the day we left for a week in a place with no internet connection. “The Bomber” is our film about Dani Dwi Permana, the 18-year old kid who walked into Jakarta JW Marriott Hotel last year, and blew himself up. And about the family he left behind.

We first watched the news on TV about a year ago – a suicide bombing at Jakarta’s JW Marriott Hotel and another one just down the road at the Ritz Carlton. There was shattered glass and debris everywhere, throngs of reporters and camera crews. We saw body bags being carried out of the hotels. But what really jolted us was CCTV footage released by the police of a gangly young man, calmly wheeling his luggage through the lobby of the Marriott … and then, the explosion. This was Dani Dwi Permana. He was just 18 years old when he died.

Why would a teenager commit such an act? In March this year, the subject surfaced during a conversation with a magazine editor friend. One of her freelancers had recently met Dani’s family. I asked if they might be interested in sharing their story in a TV documentary. The request was followed by phone calls and emails. We were a little surprised when they agreed.

Right from the start, we knew we wanted to build our film around Dani’s older brother, Jaka. He had dropped out of university to support his younger sibling after their parents split up. He had been the last person in the family to see Dani before the bombing. It was Jaka who arranged his brother’s funeral and who continues to wonder if he could have stopped Dani from becoming a mass murderer.

Before we left for Jakarta, we did not know how much Jaka was prepared to share. But he surprised us with his candor. It was as if he wanted to show us a side of Dani we never knew existed. We spent hours listening to tales of their childhood together, the games they played, the mischief they got up to, the fact that Dani loved basketball. Jaka wanted us to know there was more to his brother than that one terrible tragedy. The bomber was also a regular kid.

And this was perhaps what struck us most about their story – the ordinariness of the lives they led before their parents split up. A security guard father. A stay-at-home mother. A house in a quiet neighbourhood in a nicer part of town. Prayers at night.

Jaka’s mother took pains to tell us that her sons were good boys.

“Lots of kids do drugs,” she said. “Jaka and Dani never did.”

So what happened?

Four months before the bombing, the boys’ father, Zulkifli, was found guilty of theft and put in prison. They lost their home. Their mother, Kartini, fell apart emotionally. Unable to cope, she decided to return to her hometown in Kalimantan. Kartini took her two youngest sons with her. Jaka and Dani were left to fend for themselves.

Four months. That was all it took to turn Dani. Four months on his own, with no adult for emotional support other than the religious cleric who convinced him to make the ultimate sacrifice. Jaka continues to blame himself for not being there for his brother.

If Jaka and his family were open and willing to share, the people within their community were the complete opposite.

We asked several times for permission to film inside Dani’s mosque, but were turned down. Dani’s old friends initially agreed to meet us, and then postponed twice, before canceling at the last minute.

We spent a frustrating day at Dani’s old school, trying to convince his former headmistress to talk. We wanted to give her a chance to explain why it was tough to spot a would-be bomber among her students. Instead, she summoned Jaka to her office and spent hours interrogating him about the film, before declining to meet the crew.

It was as if the community felt tainted by its association with Dani. His crime, while not theirs, was something they did not wish to revisit, or even rationalise.

During the shoot, we were able to arrange for Jaka to meet Nasir Abbas, a former member of the al-Qaeda-linked group, Jemaah Islamiyah. Abbas is now a vocal critic of violent jihad. More importantly, he knew Noordin Top, the man who masterminded Dani’s suicide attack.

We had asked to see Abbas for some background research, but Jaka was eager to find out more, and Abbas graciously agreed to a meeting. They spoke for more than two hours. Central to the discussion was the question of whether Dani was brainwashed, whether had had a choice.

Jaka and his youngest brother, Rizki

Towards the end, we broached what we thought would be a difficult subject – religion. But even then, Jaka was surprisingly forthcoming. He admitted to being angry with God initially, but said he had come to terms with his faith.

He was unequivocal in his assertion that Islam is a good religion, a religion that teaches people not to do bad things.

Kartini too, told us that one of the first things she did after learning about Dani’s death was to pray.

Why did Dani do what he did? The answers are far more complex than we initially believed. Could someone have done something to stop him? We will never know.

What is clear though is that Jaka is determined to never let the same thing happen to his family again. Our final few minutes of footage show the boys and their mother having fun at a public pool. Jaka is holding on to his youngest sibling who cannot swim, promising he will never ever let go.