Hunter Quarries is part-owned by high-profile Maitland businessman Hilton Grugeon, who criticised the regulator and its inspectors at the time for the two-and-a-half days it took to retrieve Mr Messenger's body.

In a decision handed down last month, Judge David Russell found the prosecution had not proved beyond reasonable doubt that the quarry had failed to comply with its health and safety duty, exposing an individual to a risk of death or serious injury.

"The facts show that the cause of Mr Messenger being exposed to the risk [that killed him] was the unforeseeable actions of Mr Messenger himself," Judge Russell said.

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Judge Russell said it was the "unforeseeable" way Mr Messenger operated his 45-tonne excavator "against all instruction and training" that caused his death.

His decision said that on the morning of his death, Mr Messenger had been told to build a "bund" wall or "windrow" barrier across a quarry haul road.

Bunds were to stop machinery falling off the edge of the open-cut quarry or going into designated "no-go" areas.

Judge Russell found that instead of doing this work and without telling anyone, Mr Messenger drove his excavator over or through another bund, into a sloping no-go area.

Without building a level "pad", he began collecting and throwing boulders off the edge of the high-wall by slewing the fully extended boom-arm back and forth while sitting on unstable ground with his tracks at 45 degrees instead of facing up the slope.

Although it was considered impossible to roll such an excavator on level ground, Mr Messenger's machine toppled onto its side and he was crushed by a rock into his cabin.

The court heard that the first words Mr Messenger's step-father supervisor on the day, Brian Russell, said when he got to the accident scene was: "What the f . . . was he doing there? He wasn't f . . .ing supposed to be there."

Judge Russell said he accepted the company's submission that "no-one can explain why [Mr Messenger] did what he did".

"The only matter which is known about the tragedy is that it was done in direct contravention of the work procedures in place at the time; done in direct contravention of the direction given to Mr Messenger less than hour before; done by literally dismantling the safety barrier in place to stop people going into the dangerous area of the quarry; done without the authority to enter such an area; done in circumstances where no one had ever observed any individual simply removing bunds and barriers to enter such areas; and done by a person whose previous work record was excellent," the company's written submission said.

The case ran for some 44 days between April 2018 and June this year.

Although the prosecution pointed to the lack of a roll-over protection system on the excavator and to incomplete safety documentation, Judge Russell found the roll bar would not have made any difference and that safety rules were "implemented, observed and enforced" at the quarry.

Commenting on the judgement, Mr Grugeon said the main concern remained for the family of Mr Messenger, including Mr Russell, who still worked at the quarry.

He said Mr Messenger was a "very capable and good operator who had a great future ahead of him".

"Unfortunately, he made a mistake that cost him his life," Mr Grugeon said.

"As a company, we are satisfied with the judgement because we have always endeavoured to provide a safe workplace.

"But nothing stops the ongoing sorrow and remorse that all of us have."

Mr Grugeon called for an apology from Hunter Workers secretary Daniel Wallace, who described the quarry's safety record after the accident as "completely unacceptable", given an earlier 2005 fatality.

But Mr Wallace stood by his comments yesterday, saying that even though the regulator had lost the case, the quarry had been unable to provide "a signed copy of the "safe work" sheets showing employees had read and understood what they were supposed to do.

"The judge listed seven things he had done in breach of safety," Mr Wallace said.

"The driver was seen 'slewing' the bucket back and forth before the excavator rolled over.

"If hadn't have had the accident would anything have been done?"

"As far as I can see there are still questions to be asked."

Mr Wallace another fatality at the quarry, that of truck driver Darren Smith in 2005, was in people's minds when news spread of Mr Messenger's death.

Court records show that inspectors sought convictions over the 2005 fatality against the quarry company and its three directors - Mr Grugeon, a business partner Grahame Chevalley and Alex Badior, who was also the quarry manager.

Convictions were recorded against the company and Mr Badior, but Mr Grugeon and Mr Chevalley had the charges against them dropped during a decade long legal battle that Caselaw records as involving 13 cases in various jurisdictions, with the most recent decision coming from the NSW Supreme Court in December 2017.

Caselaw also records three other cases relating to Mr Messenger's death, including two over how much compensation his widow, Alexandra Messenger, should be paid.

Ms Messenger declined to comment about this latest decision.

A spokesperson for the resources regulator declined to comment beyond saying it was looking closely at its legal options, including an appeal against the decision.

Responding to a question from the Newcastle Herald, the spokesperson said Mr Smith's death in 2005 was not raised during the proceedings because it would only become relevant at law if the defendants were found guilty, when it would be raised during sentencing.