The WorkSafe investigation into the 2019 Whakaari White Island eruption and subsequent trial have cost taxpayers $16 million.
The 47-day trial resulted in one conviction against the company that owns the island - Whakaari Management Limited - after five other parties pleaded guilty before it went to court.
WorkSafe charged 13 parties over alleged failings on Whakaari White Island leading up to the eruption in which 22 people died. Five pleaded guilty and one was found guilty last week.
Figures released to Newshub by WorkSafe show it has spent just shy of $16 million on the case.
"It's not unusual in legal cases to have high costs and this is a particularly complex matter," said Auckland University law school teaching fellow Simon Schofield.
"If you've got QCs acting, KCs acting, then you are going to have significant costs."
Break that down and most of the cost went on external legal fees - nearly $12.5 million.
That includes work on whether the Solictor-General prosecution guidelines were met for each defendant, and what they say is years of preparation.
It's also been required to respond to a number of pre-trial court applications by various defendants - the kind of money that's always hard to recoup.
"They will never recover everything. It will be a fraction of the total costs incurred," Schofield said.
WorkSafe said "the Whakaari investigation and prosecutions have been by far New Zealand's largest and most complex health and safety investigation and prosecutions".
"This is a difficult prosecution. You're dealing with multiple defendants, you're dealing with multiple victims of the offending, and so I wouldn't envy WorkSafe's job," Schofield said.
Six parties - the government's volcano monitoring agency GNS, three helicopter companies, the tour company White Island Tours and the company that ran the island, Whakaari Management Limited (WML) - face fines of up to $1.5 million each, that's $9 million max. But there will also be payouts to victims, plus court costs against WML but also against WorkSafe for its failed prosecutions.
Sentencing takes place next February.