Police statistics for 2014 show 14,897 crimes were reported in Northland, of which 6458 were resolved - meaning an offender was apprehended and warned or prosecuted.
But Mr O'Connor said going to court acted as a deterrent, even if sentences didn't.
"I think what will happen is that, in future, police strategies will go the other way. They'll say, 'No we're going to arrest people and we're going to put them before the courts, we're going to keep them in the cells'."
Mr O'Connor said the pre-charge warning system had been initially effective, until criminals caught on to it. He had since heard complaints from police officers who were disappointed at the levels of pre-charge warnings.
Sensible Sentencing Trust Northland co-ordinator Steve Detlaff said the court system was blocked up and it was important to get serious offenders through the courts as quickly as possible. He didn't see a problem with first offenders being dealt with outside the court for non-serious offences. However, the trust believed those who committed multiple offences or violent crimes should go through the courts.
The trust was concerned that sentences handed to offenders in court were often light because prisons were overloaded.
Nationally, 62.1 per cent of offenders ended up before the courts in the year to July 31, with 37.1 per cent of offenders dealt with through non-court action and the remaining cases dropped.
To be given a pre-charge warning, offenders needed to be 17 years old or over, and to have committed low-level or minor offences with a maximum penalty of six months' imprisonment.