'Chances are they won't. Very high risk prisoners are not just let out. Think of the Moors murderers for example, they will not be released. '
But as long as that chance is still there, and as long as it is, unfortunately, there is that threat.
Only looking at this through hindsight, because believe it or not, in the US, some offenders managed to be paroled before there was a life w/o parole option.
One in particular, Kenneth Allan McDuff, served well over 30 years for a triple murder in conjunction with rape.
He slipped through the cracks.
And raped and murdered 7 more women - including one pregnant with her 3rd child - before he was apprehended.
It can happen, because parole boards are falliable and the passage of time can lessen things, including the victims' family dying or moving away and therefore not watching for the release of such criminals.
Peter Tobin is another one that springs to mind, here in the UK. This man cannot be rehabilitated. Yet even in his 60s, he was released back into the public after a particularly heinous crime - far from his first - to rape and brutally murder Angelika Kluk. Police are still gathering evidence from his former home in Bathgate, West Lothia, as he is now suspected of murdering a teenager there in the 90s, and he is being investigated for a number of unsolved rapes (he's got a long track record of this) and even the Bible John murders.