[mecsred]

Belief is not binary and can change with new evidence. You may believe it is likely someone is innocent, but should still witness all the evidence to update your beliefs. In the rare case that there is concrete and infallible evidence that the accused IS innocent, they are typically not prosecuted, or it wraps up very quickly.

[throwway120385]

This is the entire purpose of a jury trial. The intent is that the jury bears witness to all of the facts of the situation and listens to the prosecution's and defense's interpretation of those facts, and then decides whether the defendant committed any or all of the crimes they are accused of.