Chloe Hooper was at her partner’s bush block in Woodend, central Victoria, when the 2009 Black Saturday fires tore through.

“I do remember the day felt apocalyptic. There was something like 400 fires around the state. If the wind had blown differently, we would have been in trouble,” she says, almost 10 years on.

The Black Saturday bushfires killed 173 people in regional Victoria, making it the most deadly fire in colonised Australia’s history. Hooper’s latest book – a work of nonfiction called The Arsonist – focuses on two fires in the Latrobe Valley.

An investigation lead police to the conclusion that those fires were deliberately lit, and charged local Churchill resident Brendan Sokaluk, 42, with arson. Eleven people died, 10 as a direct result of the fire.

The Arsonist switches point of view between the police and prosecutors, and the lawyers defending Sokaluk. The book has the pace of a thriller (I devoured it very quickly, over an afternoon) mixed with the moral ambiguity of literary fiction.

And just like her last nonfiction book, the much lauded Tall Man, Hooper gives a cool appraisal of a hot issue. Both are accounts of a marginalised community’s pain and outrage, and the legal system’s attempts to deliver some measure of justice.

The Arsonist gives the reader reasons to feel compassion for Sokaluk – a bullied loner who was only diagnosed with autism after he’d been charged. But when the narrative switches back to the victims and the enormous distress and human toll the fires exacted, our allegiances switch.

Hooper’s account of the terrible crime that traumatised a community is even-handed and nuanced – so much so that, by the end of the book, it’s difficult to discern where her sympathies lie: victims or accused?

Speaking to Guardian Australia at a cafe in Melbourne’s North Fitzroy (Hooper and her partner Don Watson left Woodend for the city after having children), Hooper says there’s one question at the heart of the book. “In the wake of those fires, it seemed incomprehensible … Who would become an arsonist?”

After Brendan Sokaluk was arrested, Hooper suspected there might be a much bigger story, and got in her car and drove from Melbourne to the Latrobe Valley to take a look around. “It’s difficult to justify making a trip like that – I wasn’t writing for any media outlet.”

Once there, Hooper encountered wary locals. One woman – a “local-turned-security-agent, sickened by a sightseer” – tailgated Hooper until she left town.

Hooper writes, “In a crescent of near identical houses, a group of boys rode in circles, standing wolfish on their BMX bikes, knowing that something was happening, finally, in this place.”

Sokaluk’s arrest made it unsafe for him to be in the town. He was placed on remand in Melbourne.

While The Arsonist is about Sokaluk and his trial, it is also a portrait of a town in decline, in Australia’s coal country. The Latrobe Valley supplies 85 percent of Victoria’s electricity, but job losses and a shift away from coal have hit the region hard.

“Crime stories are often about dysfunction and disadvantage, and this fire took place in a town on the edge of an open-cut mine with views of power stations in every direction. So fire is a constant in that landscape,” Hooper says.

She describes Latrobe valley as “the forgotten fire”; much of the Black Saturday news coverage focused on Kinglake and Marysville, and reporting restrictions on Sokaluk’s trial meant that the public didn’t hear much about it.

Hooper herself didn’t attend the trial. She started work on the book a couple of years after that initial visit, and a lot of the narrative is a recreation, using court records.

“You know what you’re going to find, and it took me into areas you might not have chosen to delve into. I don’t know if I would have set out to write a book in coal country. It’s not a polemic about climate change but I am interested in the sociology of true crime and this moment in history and where we live.”

The decline of coal towns, poverty and climate change all form the backdrop of The Arsonist. But in many ways it’s easier for a community to go through the mechanisms of punishment and justice; having someone to blame for the fire rather than confront and deal with other more amorphous culprits such as climate change or corporate negligence.

“I tend to think he [Sokaluk] did light the fire – and a judge and jury have found that. [But in] the fires that day, 173 people were killed and 160 of those people died because of failures in our [power] grid – and we don’t have a lynch mob going after the directors of our power companies. But there is this person who is intellectually disabled, who does become a monster in our imagination.”

Hooper, now 44, has built an international fan base after her first novel, A Child’s Book of True Crime (2002) was shortlisted for the prestigious Orange prize. Her switches between writing fiction and nonfiction have “been random to me”, but she is interested in working on a novel next.

“I often think that fiction and nonfiction require slightly different muscles. For me, nonfiction is easier to write with small kids. I’m not able to daydream in the same way I could with fiction. I needed concrete facts that I can hold onto and describe.”

But now that her children are 4 and 7, she says, “I’ve started thinking a bit more about writing fiction again. It’s a relief to enter that space again when you’ve been in the hyper-real. And imagined characters are easy to deal with.”

• The Arsonist by Chloe Hooper is out on 15 October, through Penguin Random House