A former federal prosecutor dissects the “culture”of prosecution and the dangers of seeing the constitutional rights of suspects and defendants as barriers to justice in “Confessions of an Ex-Prosecutor.” :

“American criminal procedure, as developed during the four-decade retreat from the Warren Court’s recognition of defendants’ rights, encourages prosecutors to argue that rights are irrelevant. The argument goes by genteel names like “harmless error” and “lack of prejudice” and “immaterial,” and it is omnipresent in modern criminal procedure. As a prosecutor, it was my job on dozens of occasions to invoke those doctrines to assert that even if defendants’ rights were violated, those violations didn’t matter.

Take search warrants, for example. Under most circumstances, the Fourth Amendment requires police to get a warrant before they make forcible entry to your home search it. May police officers lie to a magistrate to get that warrant, or deliberately omit information that contradicts the evidence they offer? No, says the Supreme Court—that would violate your rights. But the violation only has a remedy if the lie is material—that is, if the warrant application, stripped of the lie or supplemented with the deceitfully omitted information, would no longer be enough to support probable cause. If you identify a lie that’s immaterial, you’re not even entitled to a hearing on whether it’s a lie in the first place.

So when a defendant discovers that law enforcement agents have lied to get a warrant, a prosecutor has every incentive to argue that the lie didn’t matter, that the evidence was strong enough without it to get the warrant. The prosecutor will be making this argument in the context of a search that did turn up incriminating evidence (the defendant wouldn’t be making the argument if it didn’t), which tends to bias judges towards upholding searches. After all, the judge thinks—wasn’t the cop’s suspicion proved right? Moreover, probable cause—the proof necessary to support a warrant—is a very relaxed and inherently subjective standard, requiring only a “fair probability” that evidence will be found. The practical effect is that law enforcement can lie in warrant applications with relative impunity, and it’s a prosecutorial duty to think of ways to explain how those lies are irrelevant.

On the other hand, prosecutors are encouraged to think differently about lies by mere civilians. If federal agents lie about you to a magistrate to get a search warrant, the question is whether the lie did actually make a difference. But if you lie to federal agents, the standard is far less forgiving. The materiality of a false statement to the federal government is measured by whether it is the sort of statement that could hypothetically have influenced the government’s decision-making, not whether it actually did. Thus prosecutors are trained to treat defendants’ wrongdoing harshly and government wrongdoing leniently.”