Here's a scenario for you to ponder, and hopefully respond to. Hows about we get some discussion going here?
You're charged with a crime you didn't commit. In actual fact, someone framed you. Let's say, a murder. Someone framed you for murder. The person who framed you was very smart and they managed to remove all evidences of their guilt, and substitute those evidences for evidences of your guilt.
So, you're arrested. You under-go psychological examinations. It's found that you're very capable of going to trial. You show absolutely no signs of mental defect. (What ever that means.) So then you go to trial. The prosecution starts laying out the evidence against you, and it's damning. You sit there with your jaw on the floor at the amount of evidence against you. They somehow got some DNA evidence against you!
When it's time for the defense to present, you have no alibi, you have no counter evidence. You have no reasonable doubt. You're entire defense is "Honest! I didn't do it! Please, you have to believe me!"
In the world there are two people who know in actual fact that you didn't commit the crime, it was the other guy: you and him. Everyone else hears the evidence and has to judge on that. Perhaps some people know you and say "[S]He could never do that!" (But then think of all the people who get locked away for murder who's neighbours say "He was a quiet man who seemed harmless. This took us all by surprise.")
(If you think that everyone who's in jail is guilty, you're living in a freaking dream world! Even in Canada due to interrogation methods there are people who are locked away because they confessed to a crime that they didn't commit. And let's not even talk about other nations!)
So, tell me, what should people believe? Should people believe you just because you say you didn't do it? Should people believe the evidence? What should the jury do? What should the judge do?
At what point do you accept the evidence and say "Given the evidence, it's clear I'm as guilty as sin."? Does this mean you refute the results of the psychological tests? Do you continue to be adamant about your innocence?
In other words, how much stock do you put in the evidence?
What should happen? Should you be let go? Should you spend your life rotting in prison? Or, just 25 years? Or fried?