They've been convicted on evidence, they can appeal on evidence, they can be released on evidence, the burden of proof is never on them. Shit Happens, but you can also be struck by lightning and realistically your odds of being sentenced to death for a murder you didn't commit are on par with those. We don't deal with vagaries, we deal only with cases, individual cases, always, always, always individual cases.

As for humane treatment in prison, that is totally unrelated in every way from how many of them are innocent, prisoners are treated humanely because hurting them achieves little but the debasement of civilization. First and foremost prison exists to protect society, then to punish where such punishment might achieve something and is humane, never for it's own sake.

To release prisoners of a certain percent arbitrarily and unspecifically being innocent, one would have to justify conviction on those same grounds, if 25% innocent was good enough for release, would 50% of domestic abusers being murderers be grounds for imprisonment on murder?

This is a nonsensical and pointless rhetorical argument, irrelevant because conviction can only be done to an individual person on an individual case. If we found out 10% of DNA prints gave false answers, that's not grounds for release when 8% wouldn't be, it's grounds for appeal, nothing else.