New Zealand is entering ''scary territory'' through a new law which allows indefinite detention of certain offenders who have already served their sentence, Associate Prof Colin Gavaghan warns.
Protecting citizens from dangerous offenders was clearly an important duty, but questions remained about whether the new public protection orders (PPOs) were the ''most effective or proportionate'' way of achieving this, he said.
A new report by University of Otago researchers on the role of preventive detention raises ''serious concerns'' about the new law.
Funded by a New Zealand Law Foundation grant, the report traces a trend towards judicial measures that aim not just to punish crime, but to prevent its recurrence.
This trend has continued with the contentious Public Safety (Public Protection Orders) Bill becoming law late last week.
Prof Gavaghan, of the University of Otago law faculty, is one of the authors of the report, with Dr Jeanne Snelling, and Prof John McMillan.
Supporters of the legislation had indicated that public protection orders would be a rare, last-resort measure, applying to only one or two people a year. The university report did not entirely reject the possibility that such detention might occasionally be required to protect citizens.
But vigilance was needed to ensure such orders ''don't become a more routine, knee-jerk response to public fears about certain kinds of offenders'', Prof Gavaghan said.
Other civil and criminal measures were ''oriented towards future risk'', including preventive detention and extended supervision orders.
But the new PPOs meant people could be locked up, possibly forever, based not on crimes they had committed, but because of ''predictions about what we think they might do in future''.
That was ''a pretty big step for a society like ours to take'' and moved into ''scary territory'', he said.
People charged with deciding about PPOs would be under ''a lot of pressure'' and could practise defensive management, aimed at avoiding the risk of a released person committing some future crime.
The report also asked how accurately ''future dangerousness'' could be predicted, noting concerns about ''contested methodologies''.
One solution could be to establish an independent risk assessment body, perhaps along the lines of Scotland's Risk Management Authority, which sought to ensure that decisions about potentially dangerous offenders were based on the best independent evidence.
