When a criminal robs or even kills someone, he or she does so knowing they are breaking the law, and there are remedies for punishment. However, when a prosecutor breaks the law, he is doing so in the name of upholding the law, so when that happens, what he or she is doing goes to the very heart of the system. What they are declaring is that the entire system is a lie, and if that is true, then we have no moral or even legal basis upon which to prosecute real lawbreakers.
Furthermore, unlike private citizens, prosecutors rarely are punished. To date, even though we have seen example after example of prosecutors charging and getting convictions on people they knew to be innocent, not a single prosecutor ever has faced punishment stronger than a sanction, a mere slap on the wrist.
(In the case of Michael Nifong, the infamous prosecutor in the Duke Lacrosse Case, he was disbarred and spent one day -- one day -- in jail for lying to a judge. He never had to worry about being tried for obvious crimes, nor did he ever lose a penny in the pension he now receives. The people he wanted to put on trial faced 30 years in prison if they were convicted.)
The following account given by Jacob Sullum in Reason is chilling. Prosecutors in Louisiana had exculpatory evidence, withheld it, and put a person on death row they knew to be innocent. Ultimately, the evidence was found and John Thompson ultimately received a new trial and was acquitted.
Make sure you read the story. I will leave readers with Sullum's last paragraph:
The Supreme Court has ruled that local governments can be held liable for failing to train officials in their constitutional responsibilities when the need is "obvious," as with teaching police officers the proper use of deadly force. The need for prosecutors to respect defendants' due process rights is no less obvious. And since prosecutors themselves have absolute immunity for their trial-related misconduct, the threat of lawsuits against their employers is an important safeguard to prevent the pursuit of victory from trumping the pursuit of justice.