What does 'the presumption of innocence' mean?

I'm interested in the semantic content and coherence of a "presumption of innocence" in our legal statutes. We have legal rights including a presumption that we are "innocent until proven guilty." Since guilt is legally proven after the crime (say, a murder) is committed, do we say that the person became guilty of murder at the time of conviction? That seems absurd since the convicted murderer was inside a courtroom and not committing the crime at the time of the ending of the presumption of guilt.

Lawyers and legal scholars say that this presumption is only towards legal guilt or innocence and not actual guilt/innocence of the crime. I'm not sure that interpretation would be all that philosophically kosher. Still, what happens when a conviction is overturned? Say a person had been convicted in a court of law for a crime, X. Later, evidence surfaces that there was prosecutorial misconduct and that it warrants a dismissal of the convict's case. Do we say that the (ex)convict has his conviction overturned and thus had never been (legally) guilty in the first place?

That don't seem satisfying at all. First of all, that seems like a case of spooky backward causation. How could actions in the present change past judgments? Second, we would have to say that he is innocent even though the courts had, at that time, proof of guilt beyond a reasonable doubt. Thus "proof beyond a reasonable doubt" cannot be the ultimate standard for guilt in law because you can have evidence for it and still be legally innocent if and when your case is later overturned by further revealed evidence.

I think Wittgenstein made a similar point about the difference between the makers of truth (facts) and the evidence of truth. The evidence of truth cannot provide the grounds for truth; only the facts themselves can provide it.

But if evidence cannot be the truth-maker of legal statements then that would render our legal judgments incoherent. Should we say that a person who had their convictions overturned had once been guilty of the crime but is now innocent of that same crime? That's crazy talk even a lawyer might find indefensible and incoherent. If so then they don't seem to deserve any restitution for "false" imprisonment even in cases where it's discovered later on that there was gross prosecutorial misconduct. In fact, legally, there couldn't be such a thing as "prosecutorial misconduct."

The heart of the matter seems to be that whether or not someone is guilty of an act is a not a tensed matter, it's untensed, while available evidence is.