I just want to clear up some confusion solely around the notion of innocent until proven guilty.
Let's say A murders B. Long before trial, and most certainly afterwards as well, A is guilty. That is a fact that cannot be altered. If the court finds A not guilty, A's still guilty. If we presume he's innocent, or even worse, assume he's innocent, the fact that he's guilty remains. It's the one unalterable fact that remain no matter what anyone says or does.
However, let's say we don't know whether A is guilty. Guess what, either he is or he isn't. Which way do you want to go? Do you want to assume that he's guilty thereby placing the burden of proof on A--to prove he's not guilty, or do you want to presume he's innocent thereby placing the burden of proof on the prosecution?
Courts have decided. They place the burden not on the defendant but instead the prosecution. That means the courts have decided not to assume he's innocent but rather presume he's innocent. It says nothing about his innocence. His innocence is reality dependent. Remember, if A in fact murdered B, he is in fact guilty, but we can still assume or presume innocence.
In court of law, a defendant is presumed innocent until proven guilty. That neither means he's innocent in the beginning or truly guilty at the end. Proven guilty is a confusing notion...it assumes guilt, but remember, it's just a finding. Case in point: A murders B. C is mistaken for A. A is innocent, but he is charged. They don't assume A is innocent, but they do presume A is innocent; when he is wrongly convicted (remember, he's actually innocent), the court will find him guilty and people will say he was proven guilty, but being proven guilty (in reality) is a superset to being proven guilty in a court of law.