Well, I'm confused then.
Law enforcement gathers evidence regarding X. They believe X to be responsible or culpable in some way for crime Y. They don't believe he's innocent, they believe he's guilty of Y. Once they amass enough evidence to arrest X for Y (which is a pretty damn heavy burden of proof, given the numerous rights of the accused), they take X into custody. They hand all of the evidence to the prosecutor's office.
Once the trial starts, X is assumed to be not guilty before the court and the jury. The prosecution's entire job here is to convince the jury and the judge that X is indeed guilty of Y. The defense's job is to prove the prosecution's statement wrong--either X is not guilty of Y, or he's not culpable in the way the prosecution says he is.
So basically, the prosecution
has to assume guilt, because that's the whole purpose of them being in court in the first place. I agree this isn't fair, if it was only that one side. But that's the whole point of the rights of the accused, and having a defense side to a trial.
What does it tell you about a country who calls people criminals, when the criminals are so afraid of getting caught that they're willing to go out shooting rather than be given a trial? Are those trials really that fair, then?
What?
It's a military operation. bin Laden probably fought back for reasons other than not getting a fair trial.