A lack of evidence jailing people longer puts them or anyone off committing crime makes it difficult to use deterrence as a reason to hand out long prison sentences, a High Court judge has said.
Justice Matthew Palmer told lawyers ahead of sentencing he wanted them to come to court with evidence longer sentences actually had the deterrent effect the law told him to consider.
Days later, defence lawyers came with research showing it didn't work.
The Crown turned up with nothing.
The sentencing notes of Justice Palmer reflect concern around the lack of evidence in an area which the Sentencing Act 2002 says should be considered when judges consider how long to send people to jail.
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It follows research by the Office of the Prime Minister's Chief Science Adviser this year which studied tough-on-crime laws and found "there is no evidence of the supposed 'deterrent' effect of harsher sentences".
"On the contrary, these political decisions appear to drive up the prison population and put further costs on the taxpayer."
The High Court at Auckland last week saw siblings Chevonne Wellington, 26, and Riki Wellington, 28, sentenced for their role as methamphetamine couriers.
In reaching the sentence lengths - seven years and 13 years -
Palmer then added: "That sounds sensible but do we know whether long prison sentences deter drug offending?"
He gave lawyers appearing for the Crown and defendants a week to produce answers at the sentencing.
Palmer's sentencing notes showed the Crown relied on Court of Appeal and Supreme Court rulings on the importance of deterrence in sentencing and suggested those courts were the right place to hear challenges to the value of deterrence.
Annabel Maxwell-Scott, Chevonne Wellington's lawyer, cited studies show "long sentences are not effective in deterring others or the offenders themselves".
She produced research showing there was a higher likelihood of repeat offending for drug crimes when someone was sentenced to prison rather than non-prison sentences.
Other research showed the idea of deterrence didn't take into account those whose choices were affected by drugs, alcohol or mental illness.
Maxwell-Scott told the court "the prevalence of methamphetamine has vastly risen since it was reclassified as a class A drug" and that raised questions over whether long prison terms were effective.
Palmer said it was "important to deter commercial drug dealing" but the research presented showed it was difficult to expect longer sentences would do so.
"The principle of deterrence on its own does not, in my view, justify a longer sentence if there is nothing to suggest that it would deter."
He said the Wellingtons had given plenty of other cause under the law for the "significant" sentences they earned.
Those included holding the pair accountable for harm to the community, compelling a sense of responsibility over the harm caused, to send a message such behaviour was not acceptable and to protect the community offending by either of the two in future.
Riki Wellington, who has children aged 2 and 6, was sentenced on a string of methamphetamine supply charges involving 1.5kg of the drug. He received 13 years in prison.
Palmer rejected Riki Wellington's lawyer's claim there were no victims of his offending, saying "there are very real victims of drug offending".
"Supplying methamphetamine has undoubtedly ruined lives and communities of those to whom it was supplied."
Chevonne Wellington, who has a daughter aged 9, was already serving a three-year sentence for allowing her home to be used to cook methamphetamine. She received another seven years, to be served after her current sentence, for supply charges relating to 1.3kg.
The court heard she had first used methamphetamine aged 12 but had sought help with her addiction and was now drug-free. She was judged to have a low risk of reoffending.
Palmer rejected a bid to increase her sentence because of a 2014 conviction for offering to supply a small amount of methamphetamine. "It reflects your addiction," he said.
The Wellingtons came to the attention of police investigating the 500kg shipment of methamphetamine found at Ahipara in 2016.
Victoria University criminologist Dr Liam Martin said the theory of deterrence argued along two strands - that the wider community was put off committing crime because of long sentences and that the individual sent to prison did not commit further crime because of the length of sentence.
He said the idea the broader community was dissuaded from criminal offending was impossible to measure.
However, he said there was a large body of evidence showing individuals were not deterred by long sentences and some studies showed those people went on to commit more crime.
One research showing deterrence did work, he said: "I don't think I've ever seen a study."
NZ Drug Foundation executive director Ross Bell said: "If the deterrent effect worked, we wouldn't have the problems we do."
"Our whole drug law is built on the idea of the deterrence effect as a real thing and it works. There is so much evidence know showing it doesn't work, never has and never will."