its value in pushing plea bargains and confessions.  I suppose that could also be used in a bad way - to coerce an innocent person who nevertheless sees that the evidence is against him to plead for a lesser sentence.  

However, despite all of the potential for error that exists, I cannot think of a single example of a person who was executed in the United States who did not commit the murder or treason that s/he was accused of.

The fact that many people convicted of murder have had their convictions overturned based on DNA evidence that was not available at the time of their trials leads me to conclude with certainty that there have been executions of innocents convicted of murder. A trial is only as valid as the evidence available and if exculpatory evidence has been excluded, then innocents can die.

Many, many actual murderers plead guilty to murder every year because the death penalty is available as an option to prosecutors.

Having the death penalty on the table can also coerce an innocent person to pleading guilty to a crime, or more likely, a defendant to plead guilty to a more serious crime than s/he would otherwise be convicted of. For example, someone driving the getaway car of a bank robbery gone violently bad shouldn't face capital murder charges and plead guilty to murder as opposed to possibility of jury hearing evidence that may lead to reduced charges.

If we were to take away this option, we would be handcuffing prosecutors

Prosecutors threatening defendants with charges greater than that of the crime committed is abuse of the system.

Finally, let's just accept the fact that about 60%-70% of the American public supports the death penalty...

Support for the denalty is actually declining in America.  It's no longer the wedge issue that it once was in many states.

However, despite all of the potential for error that exists, I cannot think of a single example of a person who was executed in the United States who did not commit the murder or treason that s/he was accused of.

And I´m asking seriously, trying to understand.
I mean I remember criminal cases here in Europe with people sentenced to life later released because they were innocent. Sometimes after very long prison periods.

IIRC here in Germany everything connected with the criminal case will stay in storage even after the court sentence. Meaning that if new testing methods are developed, the evidence will still be there to be tested. For example some people were proven innocent after DNA analysis was developed.

Is it the same in the USA?
Do you store the evidence and test them - if in doubt later - even after someone was already executed?
If yes, then I can understand your certainty.
If no, then I´m having doubts.

I cannot think of a single example of a person who was executed in the United States who did not commit the murder or treason that s/he was accused of.

You wholly acknowledge that errors and fabrications occur. People on death row have been exonerated.

There are two factors that must be met in sequence for a death row inmate to be set free:

• New evidence or testimony has been revealed or discovered that proves they were wrongly convicted
  
• The inmate hasn't yet been executed

Yet, if you change the sequence of events, the same truth is revealed, but the prisoner is dead. But since dead people don't appeal their sentences, the chain of events would unlikely proceed to a post-mortem exoneration.

Your statement is flawed, and dangerously so for a police officer who knows that the system is flawed. Sure, most of the time you would be right but you would never know when you were wrong because in the act of execution, you silence any motivation to uncover the truth and you destroy the evidence.

However, despite all of the potential for error that exists, I cannot think of a single example of a person who was executed in the United States who did not commit the murder or treason that s/he was accused of.

Please allow me to introduce you to Larry Griffin, well on his way to becoming the first confirmed wrongful execution in the history of the United States.  (This is not to say that there has never been another; but this time, pretty much everyone agrees.)  While Mr. Griffin's life history proves that he was definitely a bad apple, he was not sentenced to die or actually executed for being a bad apple, something which still presently does not violate any known law all by itself, let alone support the special circumstances all by itself to support a lawful capital sentence.  Mr. Griffin was, instead, executed for a murder that it now appears increasingly certain (to everyone but the prosecutor who will end up with Mr. Griffin's blood on his hands and conscience), that Larry Griffin did not in fact commit.  Of course, the "investigation is still ongoing" but frankly, there's not much left to investigate since both Mr. Griffin and the primary eyewitness used to convict him are both dead; except of course, an investigation into how the State of Missouri can actually insulate itself from both the legal liability and the utter undermining of its capital punishment system if it admits that, yes, it executed an innocent man.  

However, if the Streamlined Procedures Act of 2005 continues towards passage at the rate it is racing through both the House and Senate, Mr. Griffin will eventually become just another another statistic of the "mistakes" of the (in)justice system where capital punishment is concerned.  Given how little hell has been raised by progressives over the Griffin case, it seems that this type of collective "shrug" in response to the possibility of wrongful execution is where the country is heading.