Especially if you screw up a death penalty so bad you end up defending yourself in the presense of the Supreme Court of the United States of America.
John Holloway at Slate examines Connick vs. Thompson, which will be heard before the SCOTUS tomorrow.
In 1995, Esquire photographed him, for a piece on the death penalty, standing confidently in front of his desk with one of his favorite office decorations: a 12-inch-high, battery-powered (and operational) electric chair, complete with the mug shots of the five men he had personally prosecuted successfully in capital punishment cases. All five have subsequently been released or had their death sentences commuted to life due to procedural problems in their trials.
The plaintiff, the wrongfully convicted party, released after 18 years on death row and "acquitted in 35 minutes" once all the evidence and witnesses in the case were heard. Yes, he won his lawsuit. For an awful lot of money.
Now on defense, "prosecutors should have absolute immunity from suit—that there simply are no circumstances serious enough to allow private citizens to recover damages from the DA's office."
No circumstances serious enough. Because the state executing an innocent man isn't considered serious circumstances.