...The Constitution of the United States of America guarantees us that we are to be assumed innocent, until proven guilty...
That is the way it should be and the way many people think things are, but not reality.
Prosecutors are supposed to drop cases if they learn that the accused is innocent, but this does not happen to my knowledge.
Actually when people are innocent, lawyers many times will advise their clients to make a deal with the prosecutor and plead guilty to some lesser charge. And not try to fight it. The lawyers know how "the system" works!
The thing which really shows how our "justice system" works is rape cases along with the later use of DNA testing to review these cases. Many people who were serving time in prison for rape were later proved to be innocent by DNA testing! (Which was not available when the crime occurred.) Here is the shocking reality of this...
http://www.innocenceproject.org/Content/342.php
Then even today, the "justice system" will sometimes not allow accused people to be DNA tested! Why? I have no idea. I guess they are not in the business of finding the truth?
(I like to read non-fiction books (real world stuff) and like books written by lawyers. They spend all day writing, so are quite good at it, and can write some pretty interesting books!)