( 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 can not 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 .
Bob Barr : The parole board 's denial of clemency to John Davis was wrong ruling . Barr : Was allowed to be executed despite significant doubt about his guilt . Davis , rather than innocent till proven guilty , had to prove innocence , Barr says . Barr says he supports death penalty but not when it 's on skimpy , unreliable evidence .