The trial of former Sydney schoolteacher Chris Dawson illustrates guilty verdicts in a circumstantial murder case may be rare, but experts say circumstantial evidence can be "extremely damning" — if it all lines up.
The body of his first wife, Lynette Dawson, hasn't been found after she vanished from the city's northern beaches in 1982.
As the ex-rugby league player's barrister put it in the final days of the trial, there was "not a skerrick of scientific or forensic evidence" to suggest the now-74-year-old killed her.
In the NSW Supreme Court this week, Justice Ian Harrison spent five hours painstakingly weighing up all the circumstantial evidence to suggest otherwise, ultimately finding Dawson guilty of murder.
Even when there is no evidence involving a body, the criminal standard of beyond reasonable doubt must still be met, Arlie Loughnan from the University of Sydney said.
"That means that the totality of evidence, the sum of evidence, has to satisfy the judge or jury to this very high criminal standard," the criminal law expert told Radio Sydney.
Circumstantial evidence could include things like Dawson's statements after the fact, his behaviour or his whereabouts at the time.
Professor Loughnan said this type of evidence can help "paint a picture".
"When you're producing evidence ... you're looking to reconstruct events that happened in the past, and in this case, obviously, a long time in the past," she said.
"That means that you're looking to be able to explain everything that happened or take into account everything that happened."
Early in his judgment, Justice Harrison explained that if there existed a reasonable possibility Lynette Dawson was alive after January 8, 1982, when the Crown alleged she was murdered, Dawson was entitled to be acquitted.
In an attempt to show this, the defence team suggested Ms Dawson may have abandoned her family after her trust was broken because of Dawson's "relationship" with their teenage babysitter, JC.
They pointed to alleged sightings by five witnesses and phone calls from Ms Dawson that Chris Dawson claimed he received after she went missing, along with evidence about suggested purchase activity on a joint bank account.
But the judge rejected the sightings as fabrications, unreliable or too "frail", and found that Dawson "lied" about the reported phone calls.
The failure of key defence elements seemed the first hints of a guilty verdict during the lengthy judgment.
The judge also concluded Dawson himself was the "sole author" of the bank card evidence.
Rick Sarre, Emeritus Professor of Law and Criminal Justice at the University of South Australia, said the case was unusual because of how long ago the crime occurred, but also the role played by The Teacher's Pet podcast.
"There's nothing wrong with a circumstantial case, it's just that much more difficult to get a verdict beyond reasonable doubt," he said.
Professor Loughnan said what's known as the "CSI effect" in the trade has created an expectation there should be forensic evidence in every case.
Professor Sarre agreed that the "CSI effect" typically said forensic evidence becomes far more conclusive, but it wasn't a "slur on the justice system" to describe a case as being only circumstantial.
"Circumstantial evidence can be extremely damning if all those circumstances line up, and that's what Justice Ian Harrison said it did in this case."
That Dawson's case played out as a judge-alone trial gave observers a far greater insight into the reasoning behind findings in the judgment, compared to the behind-closed-doors deliberation involved when a jury is returning a verdict.
Dawson's legal team has flagged a "probable" appeal.
Professor Sarre expected that process to involve reviewing "every last sentence" uttered by the judge, in the hope of finding "some flaw in his reasoning".
Justice Harrison said the evidence in Dawson's case doesn't reveal how Lynette Dawson was killed, whether her husband had assistance, or the location of her body.
None of the circumstances could establish guilt when considered alone.
But having considered the circumstantial evidence as a whole, Justice Harrison said he was satisfied beyond reasonable doubt Dawson's guilt was "the only rational inference" to be drawn.
In August 1980, one of the most well-known circumstantial cases began to unfold when Michael and Lindy Chamberlain took a camping holiday in the Northern Territory.
Their nine-week-old daughter, Azaria, vanished from the family tent at Uluru and Ms Chamberlain told police that a dingo had taken the child.
NT police insisted, instead, that she murdered Azaria in the family's car and the Supreme Court indicted Ms Chamberlain on a charge of murder.
She was found guilty by a jury and sentenced to life in 1982 despite limited evidence — which was later discredited — including what was claimed to have been blood under the dash of the car.
The mother was exonerated in 1986 but it wasn't until a fourth inquest more than 30 years after the disappearance that a dingo was officially deemed responsible.
It was a case invoked by Dawson's own lawyer, Greg Walsh, outside the NSW Supreme Court following this week's verdict.
"Miscarriages of justice can occur, as we know in the Chamberlain case," he said, citing expert evidence from the Azaria Chamberlain matter.
Dawson spent his first nights in custody in the Surry Hills Police Centre, in Sydney's CBD, and Silverwater prison in the city's west.
Mr Walsh returned to court on Thursday with Dawson, who was wearing a prison-issue green tracksuit, and told the judge his client had been subjected to death threats in custody.
The lawyer told journalists outside that he decided against making a bail application, which would have been "doomed for failure".
Mr Walsh said he was still analysing the judgment of some 260 pages, but some aspects already came to mind as grounds for appeal.
For example, the judge's finding there was an intention to kill — despite what Mr Walsh said was "a complete absence of any such evidence".
Dawson is shocked, upset and has "shut down", but continues to assert his innocence, Mr Walsh has said.
A sentencing hearing was set for November 11.
Dawson has, according to his lawyer, surrendered to the possibility of spending the rest of his life behind bars.
