Private prison operator Serco says a full search of Mount Eden prison, launched after videos appeared online showing inmates taking part in organised fights, has uncovered a cellphone.
The company's director of operations Scott McNairn says the search started on Monday and so far one cellphone and a charger had been found.
He said the cellphone would now be subject to an inquiry into the fights.
Mr McNairn said it was about halfway through the search and aside from the cellphone, some prescription medication, and extra bedding had been found.
He said no illegal drugs or alcohol had been found at this stage.
The company was serious about fixing any issues at the prison, Mr McNairn said.
"We are committed to making this work and fixing any issues that [have] been raised.
"I have developed a robust operational plan which includes a full lock down of Mt Eden Prison."
Mr Davis said the inmate, named only as Evans, was the victim of a practice at Mount Eden known as dropping, which involved being thrown from a balcony.
He said the man was transferred to Ngawha prison before being sent to Whangarei Hospital, where he died.
But Mr McNairn said he had never heard of any incidents like that at the prison.
"No one has reported anything like that to us or the department, or anyone else I am aware of."
Mr McNairn said if it was occurring frequently, he would expect to see more injuries and hospital treatment, and that was not happening.
He said balconies were part of the prison design, and that was something Serco did not have any control over.
Mr McNairn had met with the Chief Inspector of Corrections and all the allegations would be investigated thoroughly, he said.
Corrections Minister Sam Lotu-Iiga said he would not be drawing conclusions until all reviews, including a coronial inquest, are complete.
''I have ordered a two-stage review. I believe that we are going to get to the bottom of this, and get some answers to the questions in order to make some changes."
Mr Lotu-Inga said his confidence in Serco will depend on the results of investigations.