Peter, Andrew and James Buttle were individually charged as directors of Whakaari Management Limited (WML) for health and safety failings ahead of the volcanic eruption in December 2019 that killed 22 people.
Judge Evangelos Thomas made the decision to throw the charges out in the Auckland District Court today.
"There is no evidence in this case of what happened behind the boardroom door at WML, he said.
"Without that evidence I can not assess what a reasonable director would have done."
This had been the brothers' third application to have the charges dismissed.
In his application on August 31, their lawyer James Cairney said there were two "glaring" faults in WorkSafe's case.
The first being that WorkSafe had treated the directors as one group in the trial and its investigation by repeatedly referring to them as "the Buttles".
"The allegation boils down to this: WorkSafe says Whakaari Management Limited breached a duty. Whakaari Management Limited was controlled by the Buttles, and if we use James as an example, James is a Buttle, therefore James is liable. It really is that crude," Cairney said.
He said the case was also flawed because WorkSafe had sought to treat any breach by WML as a breach by its directors as if it was a one-director company.
WorkSafe's lawyer Michael Hodge rejected both claims in his reply on September 1.
"While the court does of course need to consider the evidence against each defendant and reach a separate verdict in respect of each, there is a significant overlap in respect of the allegations and evidence against each Buttle," Hodge said.
"While necessarily related, the allegations against the Buttles are separate and distinct from the allegations against WML."
