Should Waipouri have ever been out?

Have just read the sentencing notes of Michael Waripouri. An awful awful killing. The victim died a horrible death.

One part that struck me was this:

You have been convicted of 91 offences, and sentenced to imprisonment for 40 of them. Relevantly, they include convictions for kidnapping, injuring with intent, various forms of assault, possession of an offensive weapon and threatening to kill. 

To be fair to Waripouri, the convictions occurred a long time ago. But what still strikes me is that someone can have 40 imprisonable offences and be out at large.