Tour company operators involved in the deadly White Island eruption could face manslaughter charges if found criminally liable for failing to protect customers, a criminal law expert says.
Police and WorkSafe are running parallel investigations into the deaths and injuries resulting from yesterday's tragedy.
Five people are confirmed dead and eight others are missing and presumed to have died. Another 31 victims remain in hospital, many of them critically injured in regional burns units.
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Police originally said they were launching a criminal investigation but later said it was "too early to confirm" whether that would go ahead.
AUT criminal law professor Warren Brookbanks told the Herald police would have to establish whether there was criminal liability for the deaths.
"We don't know the final numbers because we still have to recover bodies. But part of the investigation will be to establish whether there is sufficient evidence to bring charges of manslaughter.
"To do that they'd have to establish firstly that somebody owed a duty of care and that failure to observe that duty was a direct cause of death."
Brookbanks said there was also a duty to use reasonable knowledge, skill and care when "doing dangerous acts".
"Clearly, taking people on to an island which is an active volcano could constitute doing a dangerous act."
Another consideration would be whether conducting the tour in the knowledge of a heightened volcanic risk alert was reasonable in the circumstances, given the alert level had been elevated in recent weeks.
"The argument will be that they didn't think there was any likelihood of an immediate eruption and therefore they couldn't foresee what happened."
Police would also consider the tour companies' histories and what precautions they took to protect people, such as offering hard hats to protect against falling debris.
But given the "cataclysmic event" that had occurred, "the risks were huge and arguably would be impossible to protect against".
Any police investigation would likely take months to complete. They would need to conclude there was sufficient evidence to bring charges and that prosecution was in the public interest, Brookbanks said.
Manslaughter carried a maximum sentence of life imprisonment but a successful conviction was more likely to result in a shorter jail term, home detention or substantial fine.
WorkSafe has also launched an investigation into the tragedy under the Health and Safety in Employment Act, which could result in "draconian" penalties, including jail time or millions of dollars in fines.
Many of the injured were tourists from the visiting Ovation of the Seas cruise ship.
But Brookbanks did not believe the cruise company was likely to face charges.
"I'd say that would tenuous. It's a question of remoteness and causation. How far back do you go into attributing liability. It's possible but I would think unlikely."
Asked about the possibility that tourists had signed waivers before travelling to White Island, Brookbanks said that could protect a company against paying out for lost property.
But it would not absolve someone of liability in the event of causing death.
Auckland University law professor Bill Hodge said given there were numerous deceased victims, police could consider manslaughter charges under the Crimes Act.
"They would be looking at the White Island tour organiser, the people who decided to run the trip in spite of warnings.
"Much more likely is the investigation by Worksafe, since the vessel and the walkabout on the island was a 'workplace' (like the school canyoning at Tongariro where the high school kids were swept away."
Individuals could face up to five years in jail if convicted under the Health and Safety in Employment Act.