A common experience in teaching criminology, punishment and corrections is a denial that wrongful conviction ever occurs, or that if it does the individual in question had punishment coming anyway, or that when there seems to be an instance occurring it actually means that criminals are being let off for trivial technicalities. What do you do in these circumstances? The easy way is to accept the status quo--people who accept Fox television will believe what they see: that criminals are criminals and appeals should be abolished or severely limited.
As teachers, however, your goal is, among other things, to present facts openly and honestly, allowing students to see for themselves what evidence exists for the assertion that people are wrongfully convicted and how it is that they actually do spend lengthy periods of time in prison for crimes they did not commit. If only you had examples, students could readily see for themselves how and why it happens, how humans who participate in the process (prosecutors, defense attorneys, witnesses to crime, jailhouse snitches, aggressive interrogators, etc.) make mistakes, serious errors in judgement, lie or bend the truth, and how the entire system of criminal justice becomes a part of problem that needs to be fixed. Some obvious questions are "Where can you find data that impartially describes such cases?" "How many are there?" "Are they isolated instances or indicators of a systemic problem?" And so on.
Recently the Center on Wrongful Convictions at Northwestern University School of Law and the Michigan Law School created and are updating a Registry of known U.S. exonerations since 1989. "Exoneration" means people are freed from prison who have been wrongfully convicted. You can go there and read the lives of people who have experienced this.
Reading these cases is an eye-opening experience. What you learn first of all is that the kinds of cases leading to exoneration is very narrow--people convicted of serious crimes for whom there is a particular kind of evidence that lends itself to judicial review. This is not a criticism; it simply means that many peoples' claims that they are innocent are ignored. You have to wonder how many cases there really are involving false conviction. Immediately you have to question how it happens so frequently. So many defendants (especially those with incompetent legal counsel) are faced with the horrific choice of either pleading guilty to a crime they did not commit for a short sentence or going to trial and facing extremely long sentences if they are found guilty; what kind of a choice is that? Along with that you learn that attorney incompetence is rampant, that eyewitness testimony is notoriously unreliable, that jailhouse snitches are often used in generating evidence to define guilt or culpability, that exculpatory evidence is overlooked or ignored by prosecutors, that forensic evidence is improperly used, inappropriately assessed, or ignored, along with many other issues.
As you look at these cases and see prosecutors making motion after motion after motion to dismiss the conviction charges that led to exoneration, you see crystal clear evidence that serious mistakes happen, again and again and again. In these days of mass incarceration, mandatory minimum terms, and widespread public belief that conviction and imprisonment are the solution to the crime problem, this is a useful site that points out the serious anomalies involved in using the existing criminal justice machinery to effect justice.