THE ECONOMIST: How Prosecutors Came To Dominate The Criminal Justice System.

Another change that empowers prosecutors is the proliferation of incomprehensible new laws. This gives prosecutors more room for interpretation and encourages them to overcharge defendants in order to bully them into plea deals, says Harvey Silverglate, a defence lawyer. Since the financial crisis, says Alex Kozinski, a judge, prosecutors have been more tempted to pore over statutes looking for ways to stretch them so that this or that activity can be construed as illegal. “That’s not how criminal law is supposed to work. It should be clear what is illegal,” he says.

The same threats and incentives that push the innocent to plead guilty also drive many suspects to testify against others. Deals with “co-operating witnesses”, once rare, have grown common. In federal cases an estimated 25-30% of defendants offer some form of co-operation, and around half of those receive some credit for it. The proportion is double that in drug cases. Most federal cases are resolved using the actual or anticipated testimony of co-operating defendants.

Co-operator testimony often sways juries because snitches are seen as having first-hand knowledge of the pattern of criminal activity. But snitches hoping to avoid draconian jail terms may sometimes be tempted to compose rather than merely to sing. . . .

It is not clear how often prosecutors themselves break the rules. According to a report by the Project on Government Oversight, an investigative outfit, compiled from data obtained from freedom of information requests, an internal-affairs office at the Department of Justice identified more than 650 instances of prosecutors violating the profession’s rules and ethical standards between 2002 and 2013. More than 400 of these were “at the more severe end of the scale”. The Justice Department argues that this level of misconduct is modest given the thousands of cases it handles.

Judge Kozinski worries, however, that there is “an epidemic” of Brady violations—when exculpatory evidence is hidden from defence lawyers by prosecutors. For example, in 2008 Ted Stevens, a senator from Alaska, was found guilty of corruption eight days before an election, which he narrowly lost. Afterwards, prosecutors were found to have withheld evidence that might have helped the defence. Mr Stevens’s conviction was vacated, but he died in a plane crash in 2010.

Prosecutors enjoy strong protections against criminal sanction and private litigation. Even in egregious cases, punishments are often little more than a slap on the wrist. Mr Stevens’s prosecutors, for example, were suspended from their jobs for 15 to 40 days, a penalty that was overturned on procedural grounds. Ken Anderson, a prosecutor who hid the existence of a bloody bandana that linked someone other than the defendant to a 1986 murder, was convicted of withholding evidence in 2013 but spent only five days behind bars—one for every five years served by the convicted defendant, Michael Morton.

Related: Ham Sandwich Nation: Due Process When Everything Is a Crime.