The reasonable thing to do in such cases is to give the inmate a new trial for each of those alleged offenses. This is very basic due process.
Im genuinely repulsed by the general sentiment here (and in general) regarding incarcerated people. It doesn't help that crime based reporting has been flooding social media and news channels at disproportionate rates post 9/11's 24 hour news cycle. Its almost always an obvious attempt to evoke an emotional response too, despite crime steady decreasing over 50+ years by a fairly large margin.
This is particularly evident in American systems of modern slavery. In states like Georgia, prisoners are forced to work 40+ hours a week in places such as fast food establishments (McDonald's etc). They make well under minimum wage, and they're not allowed to miss work. Simple missteps result in punishment, loss of "good time". This means no phone calls, no visits, no venturing outside.
Such a system, if employed on everyday people, would be unthinkable. But for prisoners it's not only prevalent, we view it as a privilege. The right to work and earn money is so gracious to give to these dogs, and they should be thankful. Parole, too, is a reward, and they should be so lucky to endure 20+ years of slavery for the mere chance of getting out.
That's the thing about "due process", isn't it? It's just a phrase that basically means "the law", and the law can be changed by legislation and judges, and the law can be unjust. The phrase is nothing more than giving airs of being impartial or some check and balance against the law. This hapless fellow got his "due process".
The first element of due process is that a citizen be notified that the State is mobilizing its resources with the intention of depriving them of their life, liberty, and/or property.
Another core tenet of due process is that, once notified, you get a chance to submit evidence in your favor before an impartial adjudicator, precisely to avoid the issues in my first paragraph.
Normal parole boards in America with American due process also do not have an obligation to release people unless their guilt for further crimes can be proven beyond reasonable doubt, but they're also part of what is called due process.
You can argue this legal punishment is no good, but you can't argue for due process because he got it. In fact that is exactly what people have argued, hence this punishment being removed from the books. But in a cruel and seemingly unjust twist of "due process" of the law, the punishment was not vacated for all of those previously convicted. So if anything you would plead for an exception to normal due process here and ask that the change be retroactively applied, wouldn't you?