Troy Davis-Justice Denied

As I fell asleep Wednesday night I was waiting for the Supreme Court's decision on Troy Davis. Like many others, by the time the alert came to my phone, I was asleep and Troy Davis was dead, executed for a 1989 murder of an off duty police officer. Davis' camp fought long and hard to have the case looked at again, as Davis said he was innocent. I won't rehash all of the details of the case here, as I'm sure anyone who watches the news knows about this case. My concern falls to the effort of the "powers that be" to keep this case from being reexamined prior to Davis' execution.
Of course, innocent people have been executed from the dawn of time. We don't set out to do things this way, but our system isn't perfect. We can only process a case with the hands that we are dealt. Lack of funds of the part of the defendant can also be problematic as to seeing justice served. Court appointed attorneys do not have the resources that the state has. There are virtually unlimited funds to convict you, but limited funds to defend you, unless you are wealthy. But I digress...
How can we be sure the person that we are executing is really guilty? If your answer is that they have been convicted by a jury of their peers, please reread the last paragraph. Let's be honest, it can take a LONG time to get from conviction to the execution chamber, I believe I read somewhere it is an average of twenty years. How much can technology change in twenty years? Think about how much has changed since 2001; I bet you didn't have a cell phone then, but if you did it was the size of a briefcase. Now our phones can almost replace our home computer. Just like cell phone technology, forensic technology has changed as well. There are new investigative tools that were not available twenty years ago. At what point should these new advances be available to convicted inmates?
In every execution I would like to see a nice guilt-wrapped package, such as with Timothy McVeigh, but we very rarely get such certainty. But at the same time, we can't essentially retry each case prior to execution. We also can't simply give more attention to those who scream the loudest. We must find a middle ground. In the Davis case, many witnesses said they had lied on the stand, giving into police pressure. We also know that eyewitness testimony is the least reliable. In my opinion, that alone is enough to send up a red flag in this case. Why were the "powers that be" so resistant to review this case?
While I don't pretend to say that Davis was an angel, nor will I go as far as saying he is innocent, I do think this case needed a second look. He asked for a lie detector test before his execution, which was denied. This simple request that would have been at little to no expense to the state was denied. Why? Had Davis failed the test, end of story. Had he passed, then they would have HAD to look at the evidence in this case. I assume that was why it was denied.
No one want to see a bad guy go lose, but if we have the wrong person in jail, the bad guy is still running around in society. I think as a civilized nation, we owe it to our citizens to be sure that we are sure before we kill someone. Technology changes, people change, and the judicial system needs to keep up with these changes.