"We have been with the police dive team to survey the wreckage, which is broken up but in shallow water, and once we know the extent of the break-up we will be in a better position to continue with recovery plans.
"We know what's happened, and it will be quite a while [until we find out] why that's happened."
Investigators had interviewed the pilot, six instructors, four witnesses and had been provided police statements from the six tourists.
Mr Williams described the failure as a sudden engine stoppage, followed by a burst of flames out of the exhaust.
There could have been many possibilities for this, he said, and what the pilot had described "sounds rather catastrophic".
The investigators would focus on the engine - which Mr Williams described as popular and widely-used - and particularly a device that monitored much of the engine parameters.
Bird strike was an "outside possibility" and unlikely cause.
In incidents like this, investigators typically transported the wreckage to facilities with more capabilities than anywhere in New Zealand, and it was probable it would be analysed in Canada, he said.
The plane had been in use for about nine years - about half of that in the agricultural sector in Australia - but Mr Williams said such was the constant maintenance and certification there was likely little use in contacting its former Australian owners.
Skydive Taupo director Roy Clements said the plane had been serviced regularly, as recently as last month, and to stringent CAA standards, with no defects of any note found on previous inspections.
Mr Clements praised how his staff handled the situation.
"They were probably only doing their job, which they are trained to do, but I think at the same time, the way they dealt with it was just terrific, very calm - and that's the message we got from each of the passengers, just saying how great the instructors were."
