The defence for the owners of Whakaari / White Island is questioning why a company that approved walking tours on the volcano is not being prosecuted.
Defence lawyer James Cairney said AdventureMark, the company that approved the safety of White Island Tours, did not consult a volcanic expert during its audit.
Casey Broad, one of the leaders of WorkSafe's investigation, said AdventureMark failed to fulfil all of its responsibilities as an auditor.
Cairney's cross-examination of Broad continued for a third day on Tuesday.
He said AdventureMark, the auditing company responsible for the most-recent audit of White Island Tours, had not consulted a volcanic expert as part of its risk assessment.
Broad acknowledged that fact, noting the results of an earlier investigation by WorkSafe.
"At the conclusion of the investigation [our] recommendation was that AdventureMark had failed in their duty," he said.
Cairney asked why the company was not facing charges along with Whakaari's owners.
"WorkSafe is saying the reason there was no volcanologist, or expert on volcanic risk, was because AdventureMark made a mistake," he confirmed with Broad.
"Can you tell us why no charges were laid against AdventureMark if they're the party that failed to get a volcanic expert to consider the risk to tourists, if that was their role as WorkSafe is saying?"
Broad did not have an answer. "I was not a part of that process," he said.
Broad will later be cross-examined by the defence for ID Tours and Tauranga Tourism, which also face charges from WorkSafe.