There's tension in the air in Darwin. It's the end of what locals refer to as "the build-up": humidity is everywhere and thunderstorms are rolling in.

But the tension is highest not in the sticky midday sun, but in a small, nondescript hearing room in Casuarina, one of the city's northern suburbs.

Casuarina's everyday claim to fame is being home to the biggest shopping centre in the Northern Territory, but today it is the centre of a courtroom drama of life-and-death proportions.

The medical board of South Australia has taken the unusual step of making an immediate suspension of a doctor to protect the health and safety of the community.

Philip Nitschke has treated about half a dozen patients over the past two years.

His primary work is promoting and explaining how anyone can end their lives in a peaceful manner. It was in this capacity he had a fateful meeting earlier this year with an otherwise healthy Perth man, Nigel Brayley, who triggered the medical board's decision by committing suicide using Exit International's advice.

But the debate that raged in the Darwin courtroom was about more than the death of one man. It took in some of the biggest questions there are about euthanasia: when should a person be allowed to make such a decision for themselves, and when do doctors have a special duty to intervene to stop them?

It also may mark the beginning of the end of one of the most unusual and, some say, inappropriate medical careers in Australia's history.

The idea that someone with a terminal illness, who is suffering and in pain, should be able to end their life is relatively uncontroversial in Australia. Polls consistently show the majority of people support it.

But Nitschke remains a polarising figure, in part because his work exposes the messy edges that result when an idea is implemented. The man nicknamed "Dr Death" is also an aggressive advocate, seemingly stopping at nothing in his support for dying.

Dr Sascha Callaghan, a lecturer at the Centre for Values, Ethics and the Law at the University of Sydney, says Nitschke's apparent enthusiasm for death makes people uncomfortable.

"Deciding to end your life is tragic, and in a very deep sense human beings have always felt death is just plain bad – just by itself," she says.

"Nitschke is of a different type.  He seems to be "for" death… he doesn't seem to think that that there is a moral duty to try to talk people out of it. He gives this impression that death is a decision like any other."

Nitschke's Exit International group is radical because it allows, basically, anyone in, as long as you are capable enough to sign up and participate in the forums in a civil manner. Nitschke explained to the Darwin tribunal that unless someone is obviously mentally unwell – psychotic, or behaving very strangely – they are welcome in meetings.

When Dr Nitschke met Mr Brayley

The picture painted by the ABC's 7.30 one night in August this year was not pretty. Nitschke was supporting vulnerable people to take their own lives.

The program told how he had had an email exchange with Brayley two weeks before he died.

Brayley's wife, Lena, had died a few years ago in an apparent accident police were now investigating as a murder.

Kerry O'Neil, Brayley's friend, told 7.30:  "I think most people would assume [euthanasia's] role is quite clearly for people who are terminally ill, suffering … really in that situation where life has become intolerable in a physical sense, not for people that are just simply going through a down period in their life. Everyone goes through down periods in their life."

The Exit International forums reveal Brayley had been a "prolific contributor" to the site. Before he met Nitschke he had travelled to Hong Kong to obtain the euthanasia drug Nembutal, and explained to other users how to do so.

In fact, he "started a bit of a trend", Nitschke tells Fairfax Media, in people taking their holidays in Hong Kong and picking up a supply on the side.

On February 24 this year, Brayley attended an Exit International workshop, where Nitschke spoke to him, because he was surprisingly young for someone at the 300-strong event, with an average age of 75. Brayley told him he was attending because he wanted to be prepared for the future.

Soon after, they met again, at a rally of candidates running in the WA elections. They had a brief conversation, during which Brayley told Nitschke that his life was not going well. Nitschke asked him what was wrong, and if he wanted to talk to him or someone else, and Brayley, in Nitschke's words, told him to "butt out".

By mid-April, Bayley was one of a number of Exit members whose houses were targeted in simultaneous raids. Nitschke emailed Brayley to ask him why he had been raided, and if he would speak to the media about it. It is these emails that 7.30 obtained.

In them, Brayley says he has been targeted because of his Exit postings about successfully obtaining Nembutal: "I am not ashamed of my decision to exit or the reasons for it, however I don't honestly fit neatly under Exit's charter of supporting a terminal medical illness however i am suffering and have been now for some 9 months".

"I have sought medical and other forms of assistance but they are unable to help. All recognise and accept that my life will never be the same and that it is only going to get worse".

Nitschke later tells Fairfax Media: "I read it as him telling me he didn't want me to get involved, but other people read it as a cry for help" .

It has since emerged there were concerns about the previous disappearance of another of Brayley's partners.

Can someone who is depressed rationally choose to end their life?

The idea that, to use a phrase Nitschke repeatedly chose to use, a "serial killer" might want to end his life to avoid jail, is perhaps not so shocking.

But an innocent man hounded by the police deciding to kill himself?

As the stigma on talking about depression and suicide has lifted in Australia, more and more people have joined the battle to prevent it.

Yet the Tribunal heard there are no safeguards in place to prevent someone who is depressed from using the Exit strategies to end their lives.

Nitschke has consistently defended his view that some people who suffer depression might quite reasonably decide they do not wish to deal with that condition any longer, and end their lives. Or, they may have depressed feelings, and choose to die for some other reason, and we shouldn't prevent them making that decision because of those feelings.

He says the rate at which the elderly are prescribed antidepressant and anti-psychotic medication (far more than any other age group) means simply showing signs of depression should not rule them out of a euthanasia death.

The University of Sydney's Sascha Callaghan points out that assuming people who are severely mentally unwell can never make a decision to die or refuse lifesaving treatment can have particularly disturbing outcomes in some cases.

In one such case, a woman with anorexia, alcoholism and personality disorder had made an advance directive that should she become very unwell she should be given palliative care. This had happened, until, close to death, a UK court intervened to order she be force fed, a traumatic and dangerous intervention.

"It seems strange to us that the only people who don't seem to have the right to die when there is no further appropriate treatment available are those with an eating disorder," her parents told the court.

But the idea that someone who is at their lowest, but may well find a path to recovery, could instead make a suicide attempt they would regret (if they survive) is also deeply troubling.

Perhaps especially for psychiatrists, who pick up the pieces of such failed attempts, and see the eventual relief of survivors.

When the Brayley case was revealed the president of the Royal Australian and New Zealand College of Psychiatrists, Murray Patton, said referal and diagnosis of depression could be lifesaving. "It is of terrible concern that Dr Nitschke fails to appreciate such a fundamental clinical issue," he said.

As Nitschke faced the tribunal this failure to intervene was key.

"The concern I have is that you as a medical practitioner … if someone comes to you and is in one of those situations when they're not sure … that [you] may effectively seal the deal if you like, rather than lead them to question their own thought processes," President Kelvin Currie said.

Lisa Chapman, the Senior Counsel acting for the medical board,said, his status as a doctor meant he had an obligation to intervene, even if the suicidal person was not his patient.

And what if, she asked, Nitschke's "Dr" title gave encouragement to such a person they wouldn't feel if he were not a doctor.

But Nitschke argued he had no special obligation, other than the moral obligation anyone would have to suggest Brayley discuss his decision with someone else.

Was this the "mistake" authorities have been waiting for?

After a gruelling five hours of examination, he did admit "it was a mistake" for him to not make that suggestion again during the email exchange, and wondered if he had become desensitised to death by the sheer number of such emails he receives.

Later, he tells Fairfax Media he still thinks to do so would have been primarily about "protecting my own arse", as it would have made little difference to Brayley's decision.

"I wish I had done it for my own well-being, but I suppose if there was another unusual case like Nigel's it would be good, and who knows, it could make a difference."

But perhaps Nitschke is being a little optimistic when he says that one sentence could have made a difference to him.

On the first day of the hearing, Chapman revealed the board was currently investigating 12 other complaints against him.

Nitschke says despite his lawyer acting pro bono, he has spent upwards of $100,000 on the case.

"I can't go through this 12 more times," the says. "Sooner or later they wear you down, because they have unlimited resources."

"I don't feel like bankrupting myself to save a medical degree I rarely use".

Nitschke is tired. He looks older than his 67 years, and you have to wonder why he is fighting this battle.

Perhaps unsurprisingly, the answer is the same in life as it would be in death: he wants to go on his terms.

"At the moment I'm being depicted around the world as a failed, disgraced doctor. It damages my credibility in the political debate," he says.

But Nitschke hopes there may soon be little need to advocate for change using politics, when like-minded people can create communities online that facilitate breaking the laws that don't suit them.

So was it ever about the patients? Not for Nitschke, it seems, who freely admits his practice of medicine these days is marginal.

And maybe not for the medical board either.

After all, Chapman reminded the tribunal: "What effect would it have of not suspending him?"

It would be "a very public thumbs up" for a man who continues to advocate the most dangerous of ideas, no matter who is listening.