if you personally saw a murder you don't need no trial to know who is the killer. trial is to convince everybody else.
I don't think you know why we have trials. We don't have trials to convince everyone else. We have trials because your eyesight alone is not sufficient evidence, you need to consider all of the facts, not just what you think you saw.
If I commit act X, which is illegal, but I cannot be convicted because an error in police precedure makes some of the evidence inadmissible, it sounds like you believe that means I did not actually do X.
