Prisoners who gave evidence during an investigation into allegations of organised fighting at Auckland's Mt Eden Prison needed to have anonymity, the Corrections Department says.
Control of Mt Eden Prison was taken off private operator Serco in July after claims of violent attacks on prisoners and video footage of prison fights which was posted online.
Serco has been challenging Corrections Department's Chief Inspector's final report on the fights in the High Court in Wellington during the past two days.
Serco maintains the report relies heavily on unverified anonymous claims from prisoners, who it said were inherently unreliable.
But Solicitor-General Mike Heron, representing Corrections, said it was the Chief Inspector's prerogative to include evidence and draw conclusions he felt were appropriate.
He said the report was "fair and thorough".
"First it would have been impossible to gather many, if not all, of the statements obtained in the absence of an agreement as to anonymity," he said.
"For the same reason, prisoners were understandably reluctant to provide anything other than generalised comment."
Serco said the investigation did not confirm allegations prisoners were thrown over balconies - an act known as dropping.
Its lawyer, Hayden Wilson, said none of the prisoners interviewed by the Chief Inspector said they had seen dropping take place.
Serco argued the final report was not an accurate account of the situation at the prison.
The report itself remains suppressed.
"[We] are seeking an order that before the report is released it is revised to provide a fair and accurate account of the situation at Mt Eden, within the original terms of references for the investigation," Serco said in a statement.
Mr Wilson told the court Serco wanted to know the identities of some of the prisoners interviewed by the Chief Inspector so it could narrow its focus on where exactly in the prison problems may be.
But Mr Heron said the decision to withhold personal information was often to maintain prisoners' safety.
Justice Clark has reserved her decision.