On May 14 last year, the High Court of Australia ordered a retrial of deregistered psychiatrist Jean Eric Gassy, who had been convicted in 2004 for the murder of former SA mental health chief Dr Margaret Tobin.

Within hours, a senior medico who knew the case well was circulating an email quoting Mr Bumble and Charles Dickens — “the law is a ass — a idiot”.

His anger and frustration were unsurprising. Like many connected with the case, he was in no doubt about the conviction’s safety and was concerned that any subsequent acquittal might prove dangerous — for himself and others.

On Wednesday last week, a jury of the Supreme Court of SA took less than four hours to convict Gassy of killing his former boss, the psychiatrist whom he had blamed for ending his medical career.

Mental health professionals who have followed Gassy’s case and who understand the nature of delusional disorder will not be expecting this to be the last we hear of him.

The disorder is marked by a tendency to identify barriers as conspiracies, an endless crusading spirit to right a wrong and the belief that defeat is unacceptable. People with such disorders are likely to engage in endless litigation and it will not be surprising if Gassy seeks leave to again front the appeal courts.

The case has many remarkable aspects, including that someone trained in the arts and sciences of healing would turn to murder and that someone with all the signs of a serious psychiatric disorder was able to hold it together sufficiently to represent himself in a series of courts over some years. He managed to persuade three of five High Court judges that his conviction should be quashed.

But perhaps the most remarkable aspect of the case is how it reveals the utter inability of the legal system, bound by its archaic definitions and understanding of mental illness, to deal with defendants like Gassy — those who do not fit the traditional stereotypes of madness because they can present as lucid and rational.

The Adelaide Advertiser’s headline read “Crazed assassin Jean Eric Gassy guilty of murder — again” but the High Court decision, notably, gave no real attention to Gassy’s psychiatric state or its relevance for the case.

It is also notable that when Justice Michael Kirby weighed up the potential costs of a retrial, including the distress to Margaret’s family (who have suffered much as a result of the High Court decision), he did not include the potential for future harm if Gassy was ever acquitted and released.

Despite its formal absence from the court transcripts, Gassy’s pathology was the very core of the case — the delusional disorder explained so much, including his utter conviction that there had been a conspiracy against him, the loss of his medical registration, his dangerousness and his absolute insistence on his mental fitness to plead.

In a sense, this latter suited those anxious about Gassy’s potential for future dangerousness. If the courts had dealt with him under a mental health framework, there was a chance he would be incarcerated in a mental health facility rather than prison, with greater potential for future release and opportunity to do further harm.

The inability of the legal system to deal with the issues surrounding Gassy’s disorder deserves wide examination. Something is surely amiss when a defendant, whom many experts believe to have a serious psychiatric disorder, is allowed to appear and represent himself before the country’s highest court.

At the very least, this case should be on the agenda for discussion in forums that bring medical, legal and judicial experts together. Otherwise, the mental health issues surrounding this case will remain opaque and the medical and legal systems — which both struggled to deal with Gassy — will have missed the opportunity for learning some important mental health lessons.

Dr Peter Arnold, one of the doctors who ended up on Gassy’s “hit list” because of his involvement in the proceedings that led to the deregistration, questioned the reliability of the decision-making of juries and judges in a case where the accused is clearly psychotic but does not acknowledge it.

“The ‘ivory tower’ majority decision of the High Court is especially worrying,” he said.

“It is one thing to have 10 guilty men go free rather than have one innocent jailed for life, but, had Gassy been let out of jail, the system was truly gambling with the lives of another dozen people.

“Are juries and judges competent to safely handle cases involving psychosis, or should our legal system allow for expert psychiatric assessors on the bench to advise judges and juries?”

Another question that arises, even though it can never be answered, is whether this tragedy could have been prevented if Gassy had been compelled to have treatment early in the course of his illness.

Professor Ian Hickie, a senior psychiatrist who was a close friend and colleague of Margaret Tobin’s, said the case raised questions for the health system as well as the legal system and its definition of mental responsibility “based on 18th and 19th century concepts”.

“It’s a tragic case of a doctor with a diagnosed illness failing to receive treatment,” he said. “The essential issues behind the whole thing have never been unfolded because of the artificial divide between legal definitions of mental responsibility and modern understanding of mental illness.”

One of the many terrible ironies about this case is that so much of Margaret Tobin’s life was devoted to improving professional and public understanding about mental health. Clearly there is still much to learn.

Melissa Sweet is the author of Inside Madness (Pan Macmillan 2006), a book about the case.