On January 20, 1984, Earl Washington--defended for all of forty minutes by a lawyer who had never tried a death penalty case--was found guilty of rape and murder in the state of Virginia and sentenced to death. After nine years on death row, DNA testing cast doubt on his conviction and saved his life. However, he spent another eight years in prison before more sophisticated DNA technology proved his innocence and convicted the guilty man.

DNA exonerations have shattered confidence in the criminal justice system by exposing how often we have convicted the innocent and let the guilty...