This is something that refers specifically and only to who has the burden of proof in a trial situation. I imagine it is fairly similar in Oz, but in the US, this does not indicate that someone should be assumed to be innocent in the face of evidence compelling enough to arrest them and indict them.
"According to the U.S. Supreme Court, the presumption of the innocence of a criminal defendant is best described as an assumption of innocence that is indulged in the absence of contrary evidence (Taylor v. Kentucky, 436 U.S. 478, 98 S. Ct. 1930, 56 L. Ed. 2d 468 [1978]). It is not considered evidence of the defendant’s innocence, (empahsis mine) and it does not require that a mandatory inference favorable to the defendant be drawn from any facts in evidence."
