Because the various state bars are very, very reluctant to discipline prosecutors, the typical prosecutor knows he or she pretty much is invulnerable. Yes, they can be criminally prosecuted, but no prosecutor in the history of this country ever has been convicted of criminal malfeasance for conduct in the "line of duty," even though it has been obvious that at least in some cases, the criminal behavior was deliberate and cold. Thus, armed with that knowledge, a prosecutor knows that he or she does not operate with the same set of personal restrictions that hold back the worst behavior in other occupations.
The SCOTUS ruled in the Imbler v. Pachtman case (1976) that district attorneys or prosecutors were found to have full immunity from civil suits resulting from their government duties. Unlike the qualified immunity that was given to many public officials, the justices reasoned that while a wrongly-charged defendant would not be able to seek legal satisfaction against a prosecutor who engaged in outrageous conduct, nonetheless the immunity would better fit a broad "social good" as the court saw it.
Obviously, the court opened a huge can of worms, as it basically said that as long as a prosecutor can claim he or she was doing something within the scope of prosecutorial duties, then that person cannot be sued, even if he or she deliberately withheld evidence. Furthermore, the SCOTUS declared that
alternative sanctions to civil lawsuits against prosecutors were available to deter a prosecutor’s malicious and dishonest behavior. Indeed, the availability of bringing criminal charges against a prosecutor, as well as the availability of professional discipline by bar associations, would “not leave the public powerless.” “These checks,” said the Court, “undermine the argument that the imposition of civil liability is the only way to insure that prosecutors are mindful of the constitutional rights of persons accused of crime.”People who saw that decision as overreaching had some hope in a case Pottawattamie County v. McGhee in which prosecutors clearly framed innocent people for a murder. In fact, prosecutors claimed in their defense the following outrageous statement: there is no constitutional "right not to be framed.” That's right; prosecutors were claiming that even if they framed someone, that was OK, as the Constitution does not forbid it.
Unfortunately, the case was settled before the Supremes could rule on it. However, they gave what I hold to be a partial answer in Connick v. Thompson, declaring that the DA's office of New Orleans Parish could not be held liable for failure of its prosecutors to turn over exculpatory evidence. In other words, the SCOTUS ruled that violation of the Brady Rule inferred no particular responsibility upon the people who were responsible for violating it.
Keep in mind that most readers of this post are not prosecutors, nor are public officials. That means that the laws regarding liability are imposed differently upon them than upon those who are sworn to uphold the law and who hold special powers in bringing people to trial. The people with greater responsibility have less liability than everyone else.
If that seems to be an outrage, that is because it IS an outrage. What SCOTUS has done once again is to declare that prosecutors are a special class of people who, de facto, do not have to obey the law. And, guess what? There are lots of prosecutors who take advantage of that privilege and, surprise, surprise, violate the law with impunity.
The Rule of Law is supposed to mean just that: rule of law. A nation that has Rule of People Who Do Whatever They Want cannot survive as a decent society.