The United States of America have 13 appellate courts, known as the U.S Courts of Appeals and they are structured to operate below the U.S Supreme Court. Appeal courts consisting of three judges are tasked with the responsibility of ascertaining if the law was rightly applied at any given time in the trial court. They do not make use of a Jury (a group of individuals selected to decide if a person is guilty or not in a court room).
You need to be able to have rock hard evidence to put a criminal away depending on the jury and what they think but in most cases you need evidence that can for sure put them away.
