Why Nick McKenzie's Crossing the Line might never have seen the light of day

He could write down the true story behind the five-year legal battle between former war hero Ben Roberts-Smith and the three media outlets that had published McKenzie's expose of his war crimes, knowing it might never be published.

Or he could stay silent.

In the end, he poured his heart into telling the story of the SAS soldiers who stood up to a bully and helped expose Roberts-Smith's long-buried secrets.

And, as we now know, he and his fellow journalists were vindicated, and his account, Crossing the Lines, was published by Hachette barely a month after the verdict.

But while he was still basking in the relief of a verdict against Roberts-Smith's defamation action, he said he and his family had been subject to threats of death and violence since his book came out.

"It's been very unpleasant, but against that, there've also been many more people, especially veterans have contacted me to say thank you and they support me," he said.

"They're people who've served in Afghanistan, who've served in Iraq, served in Vietnam, whose family have served - but there is a small number of people who aren't interested in the facts and would rather issue death threats or threats of violence, and that's really disappointing."

He said there had been plenty of times he regretted ever pursuing the rumours he had been hearing about the war-front actions of Roberts-Smith; he could have walked away and focused on other stories.

"I think initially, it was a story that we approached with reluctance, for obvious reasons, because the stakes are high and it was not something you'd ever want to get wrong," he said, of the series of stories published in 2018 by The Age, The Sydney Morning Herald and The Canberra Times about war crimes committed by Roberts-Smith.

"There were certainly many times during that five or six-year process where I wish I'd never done it, because it was so stressful. And there was no guarantee - there were times we thought we were going to obviously lose, and he would triumph."

He also regretted the trauma suffered by the various witnesses who had testified against Roberts-Smith, and been subject to tough cross-examination from his barristers.

"Everyone has been stressed and traumatised by it in one way or another, and I just really feel for those soldiers who, having fought for their country bravely in Afghanistan had to endure the attacks by Ben Robert-Smith's barristers on his instructions," he said.

"I mean, that's a really low act, what happened in court in my view, where Ben Roberts-Smith knew that he was lying, he knew these men were telling the truth. He instructed his barristers to call his comrades - former comrades - liars and mentally unwell and cowards, knowing that that was false.

"One witness said they found the experience of war less stressful than the experience of court."

McKenzie began writing the book during the trial knowing it would "absolutely be spiked" if the court found in Roberts-Smith favour.

"There's no book that would ever see the light of day, and I wrote it knowing there was every chance that would never, ever be released," he said.

"It would have been a huge waste of time and effort. But I guess I also told myself, we know it's true. We know he's done these things. Okay, the court might reach a different conclusion, for legal reasons or reasons outside of our control. But I'd be so regretful if the court found what we need to be true and I hadn't bothered to tell that story in a way that it had never been told before, in a way that could give really fresh, compelling insights to people who are interested in finding out the full story."

Since the book's release, he's had the chance to talk to a range of people about the story behind the headlines, and changed the minds of those who were otherwise sceptical of the court's decision.

"People are very sceptical of journalism, sometimes for good reason," he said.

"But what the book does I think is remind Australians that ... journalists who care about their craft - and I do care about it - see themselves as public servants who want to pour absolutely everything - exhaustive journalism, integrity, everything they have - into getting it right.

"This story is about the courage of the SAS and the moral clarity that most SAS soldiers have. It celebrates the SAS for doing the right thing, I think, to see that, people recognise that that's what it's all about is really heartening to me, and important to discuss.