Editor's note: Bob Barr is a former U.S. attorney for the Northern District of Georgia and was elected to four terms in the U.S. Congress.
(CNN) -- Only the Georgia Board of Pardons and Paroles stood between life and death for Troy Anthony Davis, and the core principles of American jurisprudence should have been the board's guide. But the board ignored those principles in denying Davis clemency.
Davis was convicted in 1991 of the 1989 murder of Savannah police officer Mark MacPhail. But the trial included no physical evidence to support his conviction. The prosecution produced no murder weapon, no DNA evidence and no surveillance tapes.
He was sentenced to death on the basis of nine so-called eyewitnesses, who testified in the trial. Seven of those witnesses, however, have since recanted or materially changed their stories. The jury, for instance, relied on two people who did not witness the crime but who testified that Davis had confessed to the shooting. Since then, both have said they were lying.
The Georgia Board of Pardons and Paroles declared in 2007 that it "will not allow an execution to proceed in this state unless and until its members are convinced that there is no doubt as to the guilt of the accused."
And in the Davis case, a significant measure of doubt remained.
The U.S. Supreme Court took the extraordinary step of ordering a lower court to conduct an evidentiary hearing in the case because of the witness recantations and the absence of hard evidence. But in that hearing, the federal judge established a much higher standard of proof than the Georgia Board of Pardons and Paroles. After finding -- astonishingly for the first time -- that executing an innocent man is unconstitutional, the court then required Davis to prove that he was innocent.
Proving innocence is far more difficult than establishing doubts as to one's guilt and flips our system of criminal jurisprudence on its head. Instead of the American system's presumption of innocence and a requirement that the state prove guilt, Davis' evidentiary hearing began with the court presuming guilt and required the condemned to prove his innocence.
Even though the judge in the evidentiary hearing denied Davis a new trial, he conceded the standard was "extraordinarily high."
Davis was unable to meet this nearly insurmountable task. But while he fell short of "proving" his innocence, he established doubts as to his guilt, prompting the judge to concede the state's case against him was "not ironclad."
I support the death penalty, and have for a long time. And I am not making a judgment as to whether Davis is guilty or innocent. But surely the citizens of Savannah and the state of Georgia want justice served on behalf of MacPhail, the police officer.
Imposing a death sentence on the skimpiest of evidence does not serve the interest of justice. The Georgia Board of Pardons and Paroles did not honor the standards of justice on which all Americans depend by granting clemency. In doing so, it will allow a man to be executed when we cannot be assured of his guilt.
That was the final admirable principle standing between Davis and his scheduled death by lethal injection Wednesday. And the parole board did not uphold it.
The opinions expressed in this commentary are solely those of Bob Barr.