NO MATTER WHAT a person's view may be, there is one point on which opponents and supporters of the death penalty can reasonably agree: It is possible for an innocent person to be executed. The justice system relies on human judgment, and since human judgment is sometimes flawed, errors can—and do—occur. Police, lawyers, judges, and witnesses involved in a case sometimes make honest mistakes. Dishonesty, carelessness, and malicious acts can also impede a just decision.

Debated facts

Various efforts have been made to determine the number of people who have been wrongly convicted and either sentenced to die or actually executed while questions of guilt still remained or before new information came to light. Though such studies aim to clarify how great the risk of error is, most are mired in the same debate that surrounds all other topics related...