On a second strike, they get the ordinary sentence, and a no-parole order so they have to serve the full sentence (normally you can apply for parole after serving a third of your sentence). On a third strike, they get the maximum sentence for the offence and a no-parole order, unless the judge thinks no parole would be "manifestly unjust".
In that case, they still have to impose the maximum sentence but they can keep normal parole eligibility.
Legal experts critiqued the law heavily, pointing out that three strikes can punish quite different crimes as though they are the same. That's because each "serious violent offence" actually covers a range of actions, some of which are worse than others.
For example, an unplanned street robbery by two people, with threats but no actual violence, is an aggravated robbery, but so is a vicious, violent and premeditated armed robbery. It's simply unjust to punish these two robberies in the same way, but that's exactly what three strikes does because it automatically imposes the same consequences in both cases.
Three strikes also hands out disproportionate punishments. For example, the experts said, someone who breaks into an empty house with a knife in their possession is guilty of aggravated burglary, which is a strikeable "serious violent offence".
If that was the offender's third strike, they are supposed to be sentenced to 14 years in prison with no parole. That's a harsh punishment for what the offender actually did, and even if the judge uses the "manifestly unjust" provision to avoid making a no-parole order, they'll still serve at least 4 years and 8 months.
When three strikes is repealed, we should focus on punishment with justice. For example, if we want to incapacitate dangerous offenders with previous convictions, we can use the existing sentence of preventive detention more often.
And we'll still have our sentencing laws that allow judges to recognise aggravating and mitigating factors, like whether an offender had previous convictions, when they decide on an offender's punishment.
Serious crimes deserve serious punishment, but three strikes is a blunt tool, capable of doing serious injustice.
We should also remember that wider social policies like early intervention and social investment are a crucial piece of the puzzle. They aim to prevent negative behaviours like offending before they even begin, by investing in at-risk children to give them a shot at a better future.
Now that the Government has signalled its intention, there's room for a more finely tuned approach to punishment, one that's proportionate to each particular crime and each particular offender.
Serious crimes deserve serious punishment, but three strikes is a blunt tool, capable of doing serious injustice.
That's why it should go.
Alex Penk is the CEO of independent research and public policy think tank, Maxim Institute. This is an edited version of his latest blog. Views expressed here are the writer's opinion and not the newspaper's. Email: editor@hbtoday.co.nz