The presidential aspirations of Rick Perry are (ironically enough) bringing with them a fresh awareness of the very real existence of wrongful convictions. In the tragic case of Cameron Todd Willingham, the Texas man erroneously convicted and executed for a non-existent arson-murder, the Governor completely failed in his duty as chief executive of the state by failing to halt the execution despite being provided scientific evidence of Mr. Willingham's innocence (not that surprising, given Mr. Perry's disdain for science).
The failure of governors and/or parole boards to appropriately exercise their powers of commutation joins a long list of reasons why those charged with murder are particularly vulnerable to being erroneously tried and convicted. Those reasons include such well-known causes as dishonest prosecutors, inept defense attorneys, and political hacks posing as judges. There is one deep-seated cause, however, that cannot be eradicated with institutional reforms, and that, standing alone, is a compelling argument against the use of the death penalty. That is the fact that in murder cases (and other serious felony prosecutions), the jury does not presume the defendant innocent.
It presumes him guilty.
I want to make it clear that I am not advocating against the jury system, but against the death penalty. There are various reasons why a juror is more likely to start with a presumption of guilt in a serious case despite what the judge instructs him about the law. First, jurors are the generally more frightened of wrongly releasing a rapist, child molester, or murderer than of wrongfully convicting someone of a heinous crime. It's easy to apply the presumption of innocence to a case involving a drug sale or a commerical burglary. It is much harder for most people to give the benefit of the doubt to someone who might, if the jury erroneously releases him, commit further violent crimes.
Second, defendants in serious cases tend to look different from the jurors and to lead different lives from theirs. People are much more likely to ascribe criminal behavior to "others" than they are to people to whom they relate. Generally speaking, people who end up charged with serious criminal charges are poor, or people of color, or people with drug or alcohol issues, or people with psychiatric issues, or people who lead very different lifestyles from those of the jurors. The wrongful conviction of the West Memphis Three had more to do with the way that they dressed and the music to which they listened than to any actual evidence of guilt. The ways in which they were different from other children in the community caused the jurors to presume them guilty. Conversely, the attractive appearance of Casey Anthony ensured that the jury did not feel threatened by her, and was thus willing to give her the benefit of the presumption of innocence. The acquittal of O. J. Simpson can be at leastly partially explained by the fact that he came into the trial with a peaceful, non-threatening public persona that alleviated any concerns jurors might have about wrongfully freeing him.
Third, in capital cases the deck is further stacked against the defendant by the process of "death-qualifying" the jury. Potential jurors who can not, or who would find it difficult to, impose a death sentence cannot sit on the jury in a capital case. People who believe in the death penalty usually can (or at least claim to be able to, according to my cynical self) commit to giving a life sentence in an appropriate case. People who do not believe in the death penalty usually cannot commit to sentencing someone to die. The result is that the guilt of the accused in a death-penalty case is always decided by a jury that excludes that segment of the population that opposes capital punishment. It is, I'm sure, no surprise to learn that jurors who support the death penalty also tend to have a higher trust of law enforcement and a greater fear of crime than thise who do not. Multiple studies have established that such jurors are much more likely to convict a person charged with murder. Thus, the guilt of defendants standing trial for their lives is judged by the segment of the population most likely to presume them guilty from the beginning.
Finally, the culture has devolved from one in which 12 Angry Men was a popular dramatization of the courage and rationality expected of jurors to one in which rabble-rousing mediocrities make a fortune while tirelessly promoting the concept that anyone charged with a crime is guilty of that crime. The result is that jurors who presume the defendant guilty find their mindset celebrated in popular media, while those who actually take their oath seriously are vilified and threatened by the public. The result is that the safest thing that a juror can do in a serious case is vote for a guilty verdict.
These factors create the anomaly that the more serious the case, the lower the quality of justice the defendant can expect from his jury. This is the reason that Cyrus Vance's decision in the Dominique Strauss-Kahn case was so honorable. If a prosecutor does not believe the defendant guilty beyond a reasonable doubt, ethically he should not subject him to the palpable risk that a jury will not give him the benefit of the presumption of innocence. Unfortunately, most prosecutors presume all arrestees guilty, and few have the political courage to drop charges even in the cases in which they may harbor personal doubts about the defendant's guilt.
The fact that innocent people have been released from prison makes it absolutely certain that people other than Cameron Todd Willingham have been executed for crimes they did not commit (it is simply too unlikely that somehow students and journalists have managed to identify all of the wrongfully convicted people in this country prior to their executions). We will never know the identity of all of them because there is not much pressure to re-examine cases in which the true victim is a person who was vilified in life and forgotten in death (although sometimes there is pressure not to). The presumption of guilt with which most jurors enter into their duties on serious cases raises the risk of erroneous convictions to levels which are frightening in cases involving lengthy prison sentences, and unacceptable in cases involving the execution of the defendant. It is the inability of the average American to follow the Constitution in the judgment of criminal cases, particularly ones involving serious crimes, which is perhaps the strongest argument against the use of the death penalty.