At the end of a murderer's 21-year sentence, the prosecution can ask the court to keep him locked up for another 15-21 years, on the grounds that he will probably reoffend. If the court agrees that this is likely, it can grant an order for so-called "preventative detention". This process can be repeated indefinitely on the same grounds, but after the original period of preventative detention, extensions can only be for 10 more years at a time.

So if he's sentenced sometime next year, the timeline could be as follows:

2012-2033: prison
2033-2054: preventative detention (first time)
2054-2064: preventative detention (second time)
2064-2074: preventative detention (third time)

And so on until he dies. But in 2033, 2054 and 2064, the prosecutor will have to convince a court that he is likely to kill again if released (which would probably be quite difficult in 2064).

Is that right?