The most common error involving decisionmaking within the criminal justice process involves the use of assumptions regarding guilt or innocence, often based upon race or ethnicity, or upon profession.
Under the English form of "common law" that provided the basis for American criminal law, every defendent in a criminal proceeding is presumed to be innocent until proven otherwise through the accumulation of evidence. This presumption of innocence, a cornerstone of the U.S. criminal justice system, is occasionally ignored by law enforcement officers, prosecutors, and jurors who presume that, based upon the defendent's characteristics, that he or she is guilty of the crime.
While jurors are screened prior to a trial for indications of bias that could affect the trial's outcome, it is difficult to determine with absolute certainty that one or more jurors does not hold views that could be prejudicial to the defendent. Racial bias has historically been one of the more prevalent types of error that has occurred in U.S. history. U.S. history, especially prior to advances in civil rights, was replete with cases of black defendents being found guilty by all white juries. One of the earlier recorded of such cases was the conviction for raping a white woman of Ed Johnson, an African-American, in Tennessee in 1906. While Johnson's case was being appealed to the Supreme Court, he was lynched by rioting whites. There was no evidence indicating Johnson had been guilty.
Another well-known case involved the so-called Scottsboro Boys trial of 1931, in which nine African-American teenage boys were convicted of raping two white women in Alabama, despite the absence of any evidence whatsoever indicating their guilt.
While these two cases, and there are many more, occurred many years ago, and preceded the dawn of the civil rights era, the racial bias that was evident then remains today in some cases. A recent study by Duke University researchers determined that all white juries convicted black defendents 16 percent more often than white defendents. While that statistic may be a simplification of a broader, more complex situation, the elimination of racial bias from the criminal justice system remains a problem today, more than 100 years after Ed Johnson was lynched by a hostile mob of whites.
Assumptions of guilt based upon the race or ethnicity of the defendent is the most serious problem we face in our criminal justice system, but economic status and profession are two more. Poor defendents can not only not afford the quality of legal representation that the wealthy enjoy, but they are more likely to be presumed guilty of a violent crime than a wealthy person. Similarly, certain professions, especially politics, conjure negative images in the minds of many people -- images that may adversely affect the outcome of a trial.