The Corrections Department has paid out nearly $200,000 in the past five years for mistakenly keeping 17 inmates in jail for 438 days longer than they should have been.
One prisoner spent an extra three months at Hawke's Bay Prison on top of his sentence. The inmate received $27,000 from the taxpayer.
Figures provided to The Dominion Post under the Official Information Act show the department has paid $196,300 compensation to prisoners who were unlawfully detained since 2006.
The department has refused to reveal the nature of the prisoners' convictions or the sentences they received.
Chief executive Ray Smith blamed administrative errors for the prolonged incarcerations, in which judges or court staff had recorded incorrect dates, or when prison staff had miscalculated the time served by inmates. The errors often related to periods of remand in prison before an accused person's trial and sentencing. "Any error is disappointing, especially when the result could be that the Crown incurs a financial liability," Smith said.
But though the public were right to be concerned at the errors, they needed to be viewed in context, he said.
In the past five years the department had held more than 108,000 prisoners, but only 17 inmates had received legal settlements for unlawful detention during that period. "These figures illustrate these errors are very rare."
All compensation is subject to the Prisoners' and Victims' Claims Act 2005, which allows the Justice Ministry to deduct any victim claims, unpaid reparations, fines and amounts owed to Legal Aid. The amount of compensation was based on several factors, including the period of unlawful detainment as part of the full sentence, the steps the complainant took to protest against their unlawful detention, the suffering of shock and distress suffered by the prisoner.
Two further claims are waiting for a decision. These relate to 16 days unlawful detention at Mt Eden Corrections Facility and 77 days unlawful detention at Christchurch Men's Prison.
Human rights lawyer Tony Ellis said for the 17 prisoners who were compensated there were probably another 50 who had been unlawfully detained but who had not sought compensation.
The Prisoners' and Victims' Claims Act had deterred some prisoners from suing the department.
"There's little incentive to sue them [Corrections]. Even if they [prisoners] get some money it could be taken from them so it's becoming more and more futile to bother," Ellis said.
"Logically the situation will be getting worse because there are more prisoners. If the systems aren't improving, and they're probably not with private prisons, the likelihood of mistakes is greater."