Mangoes aren't grown in Afghanistan but across the border in Pakistan where they are transported across the desert and sold at Lakari Bazaar, a market the Taliban once used to make and store weapons.

Wegman, a former Australian special forces commando, has painted a pretty picture to describe the war machine he came to believe was fundamentally rotten, while serving in the Islamic fundamentalist stronghold.

Rolling back to the homestay he has built in Wartook, part of the Grampians National Park in South-Western Victoria, Wegman goes on to describe how the seed got diseased.

"That ego-fuelled warrior culture of trying to outdo one another and chase kill counts and validate the self by how badass you are, that's going to lead to behaviour that's definitely on the grey end of the spectrum," he says.

"I wish I could say it was as easy as finding a few bad eggs that did wrong and prosecuting them or working out the key factors of the culture that shifted and putting into place measures so that it won't ever happen again but the truth is, my experience is that I don't think there's any way to avoid it."

Wegman was part of the special forces for 13 years, the elite group of soldiers at the centre of a war crimes probe the country will today hear details of an inquiry into.

The Brereton inquiry examined 55 separate reported issues within the forces, mainly related to alleged cases of unlawful killings and cruel treatment.

"I only ever sat in preliminary hearings and none of my responses made them want to question me further and want to provide evidence in a more formal setting," Wegman said.

He did, however, windup on a mailing list from the Inspector-General of the Australian Defence Force's office which recently cautioned him against speaking to the media.

On the eve of the report's release, Wegman is clear on his motivation for breaking rank.

"I'd like every single Australian to contemplate how they were responsible.

"From the soldiers who pulled the triggers on innocent beings, the commanders that commanded them, the politicians who sent them there, right through to the average punter.

"They should see that their inaction lead to a circumstance where bad things happened and if they want to prevent that from happening in the future the best way to do that is to speak out and to share."

Wegman recalls how during his four stints in the Middle East he became disenfranchised with the organisation which disincentivised his self-reporting of mental-health decline by making it clear therapy would lead to demotion, where leadership's failure to reign in a rogue junior leader left him believing his life was in danger and where "testosterone-fuelled young men" were given guns and planes and what sometimes felt like unbridled decision-making power over who should live and who should die.

"What was being embodied was that Australian special forces were the hard-hitting element that would go anywhere that no one else would go. And why not?" he said.

"They'll go in and clean everybody up - good, bad or indifferent."

It was on Admiral Chris Barrie's watch as Chief of the Defence Force that Australia first went to Afghanistan in October 2001.

From his Mawson home this week, Barrie recalled what changed after he retired in 2002 and the returned forces engaged in combat in Afghanistan for a second time in 2004.

"The issue from a defence force perspective was a lot of the war fighting in Afghanistan was a burden for the commandos and the Special Services Regiment," he said.

"Because we have an all volunteer force, and in the United States and in Australia we dare not utter the words conscription or national service, the burden of campaigning fell to the same few people."

Barrie said that meant on some occasions people were deployed up to 12 times to serve in Afghanistan, a notion he called unconscionable.

"How do you avoid the issue of mental health from a stress disorder, the breakup of families? How do people go and spend nine months doing that and then go home and live a normal life for six months before being tapped on the shoulder and asked to go back?

"That just seems to me to be wrong, fundamentally wrong.

"Secondly, the burden of that fell entirely on the shoulders of the all-volunteer force, our community really had no other role to play in it other than reading the news stories."

After 40 years in the army, including service in the Vietnam War and the Malaysia conflict, Barrie said Afghanistan was different.

"It's war among the people," he said.

"How do you carry out a campaign which is not about inter-state conflict but intra-state conflict? How do you separate good guys from bad guys in a scenario situation in which it's hard to identify one from another?"

Unlike Wegman, Barrie said he doesn't believe the Australian population has a level of accountability to war crimes committed.

"Our community expects our war fighters to act in accordance with the law. I was the CDF [Chief of Defence Force] which had a vision of a force for good. I don't think committing the kind of war crimes that I think we're dealing with is being a force for good.

"What you are seeing is an increasing level of brutality coming forward as some of these guys keep going back and then back again and they're more and more determined to survive.

"They start to, in my words, take the law into their own hands.

"I don't think that is widespread and I think the bulk of the people I know who constitute the ADF will be disappointed and be shocked and they may be angry at what a few people have done, because it impunes all of us.

"But I don't think that's a reason not to pursue these allegations through the proper channels, they broke the law and they should be held to account."

Dr Samantha Crompvoets is the director of the Canberra-based firm commissioned to examine the special forces.

Both Dr Crompvoets and Wegman have called the term "special" problematic, Barrie disagrees.

"They are trained to operate in very small groups and accomplish missions without a lot of collateral.

"Deciding to get rid of the regiment would be mistake in the absence of any evidence that might be brought forward which said this is a smart thing to do.

"We need to bring to account those who broke the law but we also need to look at the culture, identity, organisational structures and mechanisms to see how this managed to go on from say 2010 to 2013.

"And why did it take another four years for somebody to even have a look at it?"

Barrie said the inquiry's delivery will provide an opportunity to weed out the issues and allow the Defense Force's predominantly honourable service personnel to eventually move on.

"I hope any trials that may eventuate from any war crimes are held in open court and not hidden away in the veil of secrecy like the government is quite fond of using," he said.

"I was Chief of the Defence Force when we went to East Timor in 1999 and I have to say that I couldn't be more proud of the young men and young women who served in the ADF and I think that is still true.

"That's not to say that everybody is perfect at all, but it is to say that it's a much admired institution.

"I think the Australian community has every right to expect that the much admired institution deals with this properly and openly so we can all benefit from a better ADF in the future."

Wegman and Barrie never crossed paths.

Floating for a while after graduating from a private Melbourne boys school, Wegman joined the special forces in 2004 through a recruiting scheme designed to filter out the brightest, fittest, most motivated young men from thousands who applied that year.

After eight-months full-time training, including a commando selection training course that involved cognitive assessment and about seven hours of physicals where recruits are measured against their peers, Wegman graduated a sniper, deployed for the first time in 2009.

Trained to seek out and kill, his first three deployments predominantly involved engaging the Taliban to move out of their hiding and conducting reconnaissance or intelligence-based operations.

His final stint in 2015 was a six-month stint in Kabul, part of a force protection team tasked with keeping higher-ranking officials safe as they moved through the region.

He said he saw his own morality slip over four deployments.

"What I thought was acceptable as a conscionable, good person on my first tour and what I thought was acceptable by my third deployment were two different things and I consider myself a fairly smart well-grounded person.

"But when you deploy people, when you create armies, when you create conflict the consequence is you're asking people to connect with this evil force inside themselves.

"Because when you're so fixated on facing out towards the enemy, your own enemies inside go unchecked and you don't see your own malevolence, you don't see your own hostility and violence building up".

Dr Crompvoets said good boys gone bad can't account for some of the witness statements she heard.

"There's overwhelming evidence that shows that the majority of people who are deployed aren't socialised to become evil, or sociopaths," she said.

"I think it's about the character of those individuals.

"There were definitely groups of soldiers doing the wrong thing, it wasn't a couple of bad apples, there was definitely a problem with the orchard, to extend that metaphor.

"I think there's a rush to determine whether it is just a few people or whether it was the whole culture and I think it's something a bit different to that.

"I think there was an environment that was conducive to this behaviour occurring and where there was weak leadership then that took hold and it did occur.

"The people who were perpetrators of that misconduct were exceptional at concealing their behaviour.

"I think there's a normalisation that occurs within some of those small groups where people may not have recognised it immediately as misconduct it was just the way things were done.

Dr Crompvoets said the term evil is too strong to describe the character of the worst offenders.

"It was described to me that people displayed psychopathic behaviours, absolutely not normal."

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Dr Crompvoets said she believes through the report Defence will be confident in the knowledge of why these crimes occurred and what needs to be done to ensure they don't happen again.

"There was obviously some systematic failures. While there might have been a number of people who did commit these crimes there was also thousands and thousands of soldiers who were deployed who didn't commit them. I think we need to focus on that."

Dr Crompvoets said she hoped in the weeks and months that follow the release of the report the public could have compassion toward the broader army and the special forces.

"But also want, almost demand an explanation of what went on and why," she said.

Wegman said signing up post high school because he didn't know what else to do with himself was not an uncommon sentiment among his peers.

"I fell prey to the marketing machine and the cultural mythology and all of the hero-warrior worship culture we've built up over the last century.

"I perpetuated a cycle which was: not know what to do with myself, go away with the army, have a bit of an adventure, be a bit nihilistic, get a lot of cash, come back, blow the cash, not know what to do with myself, stumble around, have a go at something - not really commit to anything - then decide to go back to the army."

Wegman returned to Afghanistan in 2010, at the peak of the counter-insurgency against the Taliban, when the overall number of foreign troops stood at 150,000.

Between December 2012 and February 2013, he described the shift in culture as a cancer which had spread through the special forces.

"Before you know it you don't even recognise yourself or the organisation you were a part of," he said.

"It was no secret that some teams were quite happy to do the things that are being alleged," he said.

Wegman said the force was authorised to shoot members of a targeted list of Taliban officials at any time.

He said members also exploited legal loopholes which allowed them to shoot anyone who they perceived to be a direct threat to their lives, whether that be through a radio they were holding or the direction they were running to higher ground, an advantage.

"I'm sure plenty of terrified farmers got shot and I'm sure plenty of soldier didn't really care that they did it.

"I certainly felt like there was a shift towards erring on the side of shooting, whereas the old adage of, 'the most important shot is the one that you don't take' kind of got thrown out the window.

"And to some extent I can see how the broken logic of a wounded alpha male could feel like that was the right thing to do.

"It wasn't from, I don't think, just some sadomasochistic desire, not wholly at least.

"Behind all the wrong doing I just see how wounded we all were to be in that circumstance to begin with."

Dr Crompvoets said there were questions around how Defence addressed mental health issues.

"There's this really difficult problem for Defence in that they absolutely want to acknowledge and assist people with mental health problems but at the same time they're restricted then in perhaps being able to deploy those people," she said.

"That creates a problem for that member because they don't necessarily want to be downgraded.

"Do they protect them and not continue to deploy them or do they acknowledge their mental health problems but not medically downgrade them?"

Wegman dodged what he felt was becoming problematic drinking and is finding peace in one of the quietest, less inhabited landscapes in Victoria.

"The healing process is not pretty, it's a slow and sometimes painful.

"Rewiring the mind and rewiring the brain and unpicking the tentacles of the army way of doing things and thinking, that's a slow process," he said.

"When you're giving people the power to kill and to execute - what does that do to people?

"And what it does in my experience is ... it's a strange thing to go through that process.

"And it's not clear to me that we know how to integrate that level of lethality all that well.

"I hope we err on the side of giving space and love and compassion to those people who have the courage to speak the truth.

"And if there are soldiers out there who have done things and might not be caught up in the investigation but are sitting there silently drinking themselves to death every night, that the collective discussion can be one around helping them heal rather than sending them to jail to suffer, because they're already in a prison inside of themselves."