They may both be law-breakers, but their offences could not be further apart.

Paul Dally tortured, raped and murdered 13-year-old Karla Cardno 20 years ago. This week, he will plead with the Parole Board to be released from prison.

Mikey Havoc ran up $20,000-plus in parking fines, many incurred around Auckland University while the popular DJ hosted bFM student radio's morning show.

Yet what the two men's cases have in common are the questions they raise about how we punish people who break the law.

New Zealand's justice system is bi-polar. Its mood swings violently between hot-blooded vengeance and gentle rehabilitation.

And, at both extremes, it is letting us down.

Havoc is the beneficiary of a law that allows judges to convert accumulated fines into community work. The argument for this - and it is mostly a good argument - is that wealthy offenders blithely incur and pay off fines without feeling any pain. But those who have less money, and their families, may suffer hardship in trying to pay fines, especially as the late payment penalties mount.

For those who struggle to pay off their debt to society in cold, hard cash, it makes sense to allow them to pay through work that benefits the community.

Where this falls down is when someone like Havoc is allowed to play the system like he plays his records.

Havoc's fines have been wiped, on the condition that he does community work - specifically, entertaining students by playing music in the Auckland University quad.

This is a man who makes his living at bFM playing music to students - and by the sound of things, enjoys his job. So his punishment scarcely qualifies as hard labour.

Some will perceive this as an abuse of community service, and of society's good intentions. Others, wrongly, will see it as an indictment of the entire system of community service, as evidence that the justice system is too soft on law-breakers.

Every time an isolated case like this brings the sentencing system into disrepute, the cries for tougher penalties grow louder.

This week, a high-profile musician who admitted an indecent act on a 16-year-old girl was discharged without conviction, and granted permanent name suppression.

Louise Nicholas, who had previously testified about sexual abuse allegedly committed by three policemen, criticised "the system" that protected the identity of an assailant.