After analyzing these cases, the researchers found that most wrongful convictions resulted from a combination of errors. The main cause in more than half of the cases -- 52.3 percent -- was eyewitness misidentification.
The next most common main cause was perjury by a witness, which contributed to 11 percent of the convictions. Other problems included negligence by criminal justice officials, coerced confessions, "frame ups" by guilty parties, and general overzealousness by officers and prosecutors.
Overzealousness can lead authorities to make careless, if unintentional errors, and cause some authorities to bend rules to get a known criminal off the street. Failure to keep an open mind can cause errors that become rubber-stamped by trusting colleagues as the case moves through the judicial process, Huff says. By the time the errors are discovered, the trail to the real offender is cold.
Public pressure to solve a case and the organizational culture of a police or district attorney's office can affect the process. While most errors are unintentional, the researchers say there are far too many incidences of unethical and unprofessional behavior.
"If you lock someone up for life, you take him off the streets, but you can later release him and compensate him if you discover that you made an error. If you kill him, you no longer have that option and you also send a message that violent solutions -- executions -- are approved by the state."
http://researchnews.osu.edu/archive/ronhuff.htm?du