( CNN ) -- A death row prisoner in Georgia has not proven his innocence , a federal court ruled , according to papers released Tuesday . Troy Davis faces execution for the killing of a Savannah , Georgia , police officer in 1989 . He has always said he did not kill Officer Mark MacPhail . The Supreme Court granted a stay of execution for him two hours before he was set to die in 2008 , and another federal court later granted him another stay as he fought to overturn his conviction . The Supreme Court last year ordered a lower court to look at the evidence again . But the U.S. District Court for the Southern District of Georgia has now found Davis has not exonerated himself . `` Mr. Davis vastly overstates the value of his evidence of innocence . ... Some of the evidence is not credible and would be disregarded by a reasonable juror . ... Other evidence that Mr. Davis brought forward is too general to provide anything more than smoke and mirrors , '' the court found . Davis can still appeal to the 11th Circuit U.S. Court of Appeals , and if that fails , to the Supreme Court again . His sister , Martina Correia , said Tuesday afternoon she had not yet had a chance to discuss the decision with Davis , who is sitting on death row at Baldwin State Prison in Hardwick , Georgia . She spoke to him a couple of days ago , she said , but they did not discuss the impending decision . `` Of course , we 're very disappointed , '' she said . `` Troy 's innocent , so we 're going to keep fighting . We 're going to appeal this decision . '' She said she and the lawyers were still reading the court 's decision , so she was n't prepared to discuss the next step in her brother 's defense strategy . Witnesses claimed Davis , then 19 , and two others were harassing a homeless man in a Burger King restaurant parking lot when the off-duty officer arrived to help the man . Witnesses testified at trial that Davis then shot MacPhail twice and fled . But since his 1991 conviction , seven of the nine witnesses against him have recanted their testimony . No physical evidence was presented linking Davis to the killing of the policeman . Supreme Court Justice John Paul Stevens ordered a federal judge in August 2009 to `` receive testimony and make findings of fact as to whether evidence that could not have been obtained at trial clearly establishes petitioner 's innocence . '' Stevens , who has since retired , said the risk of putting a potentially innocent man to death `` provides adequate justification '' for another evidentiary hearing . Davis ' case has had a dramatic series of ups and downs . He was granted a stay of execution by the Supreme Court two hours before he was to be put to death . A month later the justices reversed course and allowed the execution to proceed , but a federal appeals court then issued another stay . Davis filed an `` original writ of habeas corpus , '' which allowed him to bypass lower federal courts and make his appeal directly to the high court . What 's unusual about Davis ' case is that such action is hardly ever successful . The Supreme Court often discourages claimants from maneuvering around the lower courts whose job it is to handle such appeals . In his dissent , Justice Antonin Scalia noted that the Supreme Court had not granted similar relief `` in nearly 50 years . '' In June 2009 , Davis supporters delivered petitions bearing about 60,000 signatures to Chatham County , Georgia , District Attorney Larry Chisolm , calling for a new trial . Chisolm is the county 's first African-American district attorney . Davis is also African-American . The Georgia Pardons and Parole Board held closed-door hearings and reinterviewed the witnesses and Davis himself in 2008 . The panel decided against clemency . Prominent figures ranging from the pope to the musical group Indigo Girls have asked Georgia to grant Davis a new trial . Amnesty International has also backed a new trial for Davis . Other supporters include celebrities Susan Sarandon and Harry Belafonte ; world leaders such as former President Jimmy Carter and former Archbishop Desmond Tutu ; and former and current U.S. lawmakers Bob Barr , Carol Moseley Braun and John Lewis . CNN 's Bill Mears and Eliott C. McLaughlin contributed to this report .
NEW : Troy Davis 's sister says she is disappointed and will keep fighting . The evidence Davis presented is `` not credible '' or `` smoke and mirrors , '' court finds . Davis faces execution for killing an off-duty police officer in 1989 but says he is innocent . He was convicted in 1991 but witnesses have since recanted their testimony .