Prosecutors hold tremendous power, more than anyone other than jurors, and often much more than jurors because most cases don’t go to trial. Prosecutors and their investigators have unparalleled access to the evidence, both inculpatory and exculpatory, and while they are required to provide exculpatory evidence to the defense under Brady, Giglio, and Kyles v. Whitley, it is very difficult for the defense to find out whether the prosecution is complying with this obligation.

Prosecutors also have tremendous control over witnesses: They can offer incentives — often highly compelling incentives — for suspects to testify. This includes providing sweetheart plea deals to alleged co-conspirators and engineering jail-house encounters between the defendant and known informants.

Sometimes they feed snitches non-public information about the crime so that the statements they attribute to the defendant will sound authentic. And, of course, prosecutors can pile on charges so as to make it exceedingly risky for a defendant to go to trial. There are countless ways in which prosecutors can prejudice the fact-finding process and undermine a defendant’s right to a fair trial.

This, of course, is not their job. Rather, as the Supreme Court has held, “[A prosecutor] is in a peculiar and very definite sense the servant of the law, the twofold aim of which is that guilt shall not escape or innocence suffer. He may prosecute with earnestness and vigor — indeed, he should do so. But, while he may strike hard blows, he is not at liberty to strike foul ones.”

All prosecutors purport to operate just this way and I believe that most do. My direct experience is largely with federal prosecutors and, with a few exceptions, I have found them to be fair-minded, forthright and highly conscientious.

But there are disturbing indications that a non-trivial number of prosecutors — and sometimes entire prosecutorial offices — engage in misconduct that seriously undermines the fairness of criminal trials. The misconduct ranges from misleading the jury, to outright lying in court and tacitly acquiescing or actively participating in the presentation of false evidence by police.

Prosecutorial misconduct is a particularly difficult problem to deal with because so much of what prosecutors do is secret. If a prosecutor fails to disclose exculpatory evidence to the defense, who is to know? Or if a prosecutor delays disclosure of evidence helpful to the defense until the defendant has accepted an unfavorable plea bargain, no one will be the wiser. Or if prosecutors rely on the testimony of cops they know to be liars, or if they acquiesce in a police scheme to create inculpatory evidence, it will take an extraordinary degree of luck and persistence to discover it — and in most cases it will never be discovered.

There are distressingly many cases where such misconduct has been documented, but I will mention just three to illustrate the point. The first is United States v. Stevens, the prosecution of Ted Stevens, the longest serving Republican Senator in history.

Senator Stevens was charged with corruption for accepting the services of a building contractor and paying him far below market price — essentially a bribe. The government’s case hinged on the testimony of the contractor, but the government failed to disclose the initial statement the contractor made to the FBI that he was probably overpaid for the services. The government also failed to disclose that the contractor was under investigation for unrelated crimes and thus had good reason to curry favor with the authorities.

Stevens was convicted just a week before he stood for re-election and in the wake of the conviction, he was narrowly defeated, changing the balance of power in the Senate. The government’s perfidy came to light when a brave FBI agent by the name of Chad Joy blew the whistle on the government’s knowing concealment of exculpatory evidence.

Did the government react in horror at having been caught with its hands in the cookie jar? Did Justice Department lawyers rend their garments and place ashes on their head to mourn this violation of their most fundamental duty of candor and fairness? No way, no how. Instead, the government argued strenuously that its ill-gotten conviction should stand because boys will be boys and the evidence wasn’t material to the case anyway.

It was only the extraordinary persistence and the courageous intervention of District Judge Emmet Sullivan, who made it clear that he was going to dismiss the Stevens case and then ordered an investigation of the government’s misconduct that forced the Justice Department to admit its malfeasance — what else could it do? — and move to vacate the former senator’s conviction. Instead of contrition, what we have seen is Justice Department officials of the highest rank suffering torn glenoid labrums from furiously patting themselves on the back for having “done the right thing.”

[Footnote moved: This wasn’t the only prosecution that has had profound effects on American politics. “A revelation in journalist Judith Miller’s new memoir, ‘The Story: A Reporter’s Journey,’ exposes unscrupulous conduct by Special Counsel Patrick J. Fitzgerald in the 2007 trial of I. Lewis ‘Scooter’ Libby.” According to Berkowitz, “It is painful to contemplate how many lives — American and Iraqi — might have been spared had Mr. Libby, the foremost champion within the White House in 2003 of stabilizing Iraq through counterinsurgency operations, not been sidelined and eventually forced to resign because of Mr. Fitzgerald’s multiyear investigation and relentless federal prosecution.”

Overly aggressive prosecution also wrecked the political career of longtime Iowa state legislator Henry Rayhons. The Attorney General of Iowa charged 78-year-old Rayhons with rape for having sex with his own wife, who was afflicted with Alzheimer’s. By the time the jury acquitted Rayhons, he had withdrawn from the re-election race for a seat he had held for 18 years.]

The second case comes from my own experience. The defendant was Debra Milke, who spent 23 years on Arizona’s death row after a conviction and sentence obtained in 1990 based on an oral confession she supposedly made to Phoenix police detective Armando Saldate Jr. as a result of a 20-minute interrogation. No one was present in the room with Milke except Saldate, who refused to record the session, despite his supervisor’s admonition that he do so. When the session ended, Saldate came out with nothing in writing — not even a Miranda waiver — and claimed Milke had confessed; Milke immediately and steadfastly denied it.

The jury believed Saldate, but what the prosecution failed to disclose is that Saldate had a long and documented history of lying in court; he also had a serious disciplinary infraction bearing on his credibility: He had sought to extort sex from a lone female motorist and then lied about it when she reported the incident. It is not difficult to imagine that a jury may have been skeptical of Saldate’s testimony that Milke confessed, had it known about his track record. But the Maricopa County District Attorney’s office did not disclose this information, although it was party to many of the proceedings where Saldate had been found to be a liar.

The evidence remained hidden for two decades until an unusually dedicated team of lawyers and investigators spent hundreds of hours digging through all of the criminal prosecutions in Maricopa County during the era when Saldate had been an investigator. It winnowed down those cases and focused on those where Saldate provided evidence. And the state doggedly refused to turn over Saldate’s disciplinary record until forced to disgorge it by an order of the district judge who considered Milke’s federal habeas petition.

After we vacated the conviction and gave Arizona a chance to re-try Milke, the Arizona Court of Appeals barred any re-trial in an opinion so scathing it made the New York Times. The Court of Appeals described the “long course of Brady/ Giglio violations in this case” as a “flagrant denial of due process” and “a severe stain on the Arizona justice system” — one that it hoped would “remain unique in the history of Arizona law.” The Arizona Supreme Court recently denied the state’s petition for review, so the Court of Appeals decision stands. Maricopa County Attorney Bill Montgomery lamented that “[t]he denial of [the] petition for review is a dark day for Arizona’s criminal justice system.”

The third case is unfolding as I write these words. It involves the prosecution in Orange County of Scott Dekraai, who was convicted of having shot several people at a hair salon and is facing a capital penalty-phase trial.

The prosecution presented evidence from a jailhouse informant, Fernando Perez, whom Dekraai had purportedly confessed to. It turns out that Perez was a serial informant who had presented similar confessions. Defense counsel challenged the informant, and Superior Court Judge Thomas Goethals ordered the prosecution to produce evidence bearing on this claim. He eventually found that the Orange County District Attorney’s office had engaged in a “chronic failure” to disclose exculpatory evidence pertaining to a scheme run in conjunction with jailers to place jailhouse snitches known to be liars near suspects they wished to incriminate, effectively manufacturing false confessions.

The judge then took the drastic step of disqualifying the Orange County District Attorney’s office from further participation in the case. But this result came only after public defender Scott Sanders “wasted two years uncovering government misconduct, time that he could have spent preparing Dekraai’s defense against the death penalty.” Pulling an elephant’s teeth is surely easier than extracting exculpatory evidence from an unwilling prosecution team.

These cases are hardly unique or isolated. But they illustrate that three ingredients must be present before we can be sure that the prosecution has met its Brady obligations under the law applicable in most jurisdictions. First, you must have a highly committed defense lawyer with significant resources at his disposal. Second, you must have a judge who cares and who has the gumption to hold the prosecutor’s feet to the fire when a credible claim of misconduct has been presented.

And, third, you need a great deal of luck, or the truth may never come out. The misconduct uncovered in the Milke and Dekraai cases seems to implicate many other cases where criminal defendants are spending decades in prison. We can only speculate how many others are wasting their lives behind bars because they lacked the right lawyer or the right judge or the luck needed to uncover prosecutorial misconduct.

While most prosecutors are fair and honest, a legal environment that tolerates sharp prosecutorial practices gives important and undeserved career advantages to prosecutors who are willing to step over the line, tempting others to do the same. Having strict rules that prosecutors must follow will thus not merely avoid the risk of letting a guilty man free to commit other crimes while an innocent one languishes his life away, it will also preserve the integrity of the prosecutorial process by shielding principled prosecutors from unfair competition from their less principled colleagues.