Troy Davis is a poor poster boy for the anti death penalty campaigners, because once you look into the case he looks very guilty indeed.  He shot a man in the face an hour before Mark McPhail was killed, and the bullets from that shooting matched those taken from McPhail's body.
As the article in the OP states:
1. Of the nine witnesses who appeared at Davis's 1991 trial who said they had seen Davis beating up a homeless man in a dispute over a bottle of beer and then shooting to death a police officer, Mark MacPhail, who was acting as a good samaritan, seven have since recanted their evidence.
2. One of those who recanted, Antoine Williams, subsequently revealed they had no idea who shot the officer and that they were illiterate – meaning they could not read the police statements that they had signed at the time of the murder in 1989. Others said they had falsely testified that they had overheard Davis confess to the murder.
3. Many of those who retracted their evidence said that they had been cajoled by police into testifying against Davis. Some said they had been threatened with being put on trial themselves if they did not co-operate.
4. Of the two of the nine key witnesses who have not changed their story publicly, one has kept silent for the past 20 years and refuses to talk, and the other is Sylvester Coles. Coles was the man who first came forward to police and implicated Davis as the killer. But over the past 20 years evidence has grown that Coles himself may be the gunman and that he was fingering Davis to save his own skin.
5. In total, nine people have come forward with evidence that implicates Coles. Most recently, on Monday the George Board of Pardons and Paroles heard from Quiana Glover who told the panel that in June 2009 she had heard Coles, who had been drinking heavily, confess to the murder of MacPhail.
6. Apart from the witness evidence, most of which has since been cast into doubt, there was no forensic evidence gathered that links Davis to the killing.
7. In particular, there is no DNA evidence of any sort. The human rights group the Constitution Project points out that three-quarters of those prisoners who have been exonerated and declared innocent in the US were convicted at least in part on the basis of faulty eyewitness testimony.
8. No gun was ever found connected to the murder. Coles later admitted that he owned the same type of .38-calibre gun that had delivered the fatal bullets, but that he had given it away to another man earlier on the night of the shooting.
9. Higher courts in the US have repeatedly refused to grant Davis a retrial on the grounds that he had failed to "prove his innocence". His supporters counter that where the ultimate penalty is at stake, it should be for the courts to be beyond any reasonable doubt of his guilt.
That last point there shows that the courts decided the burden of proof was on the defense and not on the prosecution, which is basically an ass-backwards way to do "justice".
From 
this CBS article:
Davis, who is black, was charged, tried and convicted in Georgia for murdering a white police officer. He was sentenced to death in 1991. There was no physical evidence linking him to the crime. There was no DNA. There was no murder weapon found on him. Since his trial, seven of the nine main prosecution eyewitnesses against him have recanted their trial testimony. Some of these witnesses claim police coercion or harsh interrogation tactics caused them to be untruthful at trial.
Moreover, a handful of witnesses have stepped forward to claim that another man has confessed to the crime. This "other man," according to the Atlanta Journal-Constitution, is one of the two remaining trial witnesses who, not surprisingly, still claims that Davis shot the officer. The final eyewitness (of the nine we are concerned with) initially told the police that he could not identify Davis at the crime scene before later changing his tune at trial and incriminating Davis. Even during this new age of DNA there has been no great movement to resolve these legal and factual conflicts.
Short of seeing a videotape of that other fellow's confession, it's hard to imagine a scenario that more clearly calls out for a full and independent evidentiary hearing, or even a new trial, to assess the validity of the changed narrative about Davis' role in the crime. And, indeed, in an earlier time in our history it is quite likely that the federal courts would have ensured such a review. No more. The highly-politicized, step-by-step closing of the courthouse doors to appeals like this-the intentional restriction of meaningful appeals rights-may send an innocent man to his death.
When Davis' appeal on these issues made it to the Georgia Supreme Court the judges there denied him any relief and declared in a 4-3 vote that there must be "no doubt of any kind" but that the trial testimony was of the "purest fabrication" in order to warrant interceding on Davis' behalf. Got that? It takes only the absence of "reasonable doubt" to convict someone of murder but in Georgia to properly investigate a condemned man's strong claim of innocence judges have to have "no doubt" at the outset of the inquiry that the inquiry will prove his innocence. How, one dissenting Georgia justice asked, can anyone ever meet such a standard?
Even many of the original jurors when 
interviewed by the Guardian, questioned their own original decisions.
One example from the Guardian article:
During the trial, Forrest (one of the jurors) was swayed by the testimony of Dorothy Ferrell, who said she witnessed the slaying from a hotel across the street. On the witness stand, Ferrell said she was "real sure, positive sure" that Davis was the shooter.
Years later, Ferrell signed a sworn statement for Davis' lawyers that she felt pressured by police to name Davis as the shooter because she was on parole for a shoplifting conviction at the time of the trial. Forrest said reviewing Ferrell's statement weighed heavily in her decision to question their verdict.
"If I had known the young lady had issues in her past that made her susceptible to being pushed into something, I would not have put so much emphasis on what she said," Forrest said.
I don't think anybody should hang their opposition to the death penalty on Troy Davis, especially when there's a far more obvious injustice in the case of Cameron Todd Wallingham.
There are plenty of cases where the accused's guilt for the crime for which s/he is convicted is not 100% clear and beyond reasonable doubt. One case doesn't have to take attention away from another.