Sorry mate, denial of parole isn't necessarily illegal.
Parole is an early release, while you're still under sentence. Let's say you got an 9 year sentence for a crime. After a certain amount of time you'd be allowed to apply for parole ( which is no guarantee you'll get it) but if you're successful you get released, even though you may have only served 4 or so years. It works differently in different places e.g. where I live, you are eligible for parole after serving one third of your sentence.
A judge can impose a "minimum non parole" period, usually for violent offenders. So you might get 14 years for grievous bodily harm, and an 8 year MNP period ( usually you could ask for parole after 4 and a half years, but the judge is going to make you wait eight).
The "three strikes laws" in New Zealand worked by denying offenders parole. It's different from the 3 strikes law in California. In New Zealand if you got your 3rd strike you served the maximum sentence without parole - which means if you had 2 violent offenses and then a murder you served life without parole.
We actually sentenced our worst mass shooter to life without parole last year.
As I said in a previous post, I think the Dent Act and Blackgate prison were about holding people facing criminal charges indefinitely without a trial, which is a violation of the US Constitution.