UPDATE (Sept. 14, 2018, 12:35 p.m.): Since we wrote this story, Michael Cohen, Trump’s former attorney, pleaded guilty to charges from federal prosecutors in New York that implicate the president. And now, Paul Manafort — the president’s former campaign manager — has also stuck some kind of deal. That deal appears to go further than Cohen’s; Manafort has apparently agreed to cooperate with special counsel Robert Mueller’s probe. It all brings back some of these larger questions about how prosecutors use incentivized informants, whether that use is transparent enough to be just, and how trustworthy this kind of testimony is. You can read our original story, about what the research says about incentivized informants, below.

Will Michael Cohen flip? The media has been debating that question ever since the FBI raided the office of President Trump’s longtime personal lawyer on April 8. Cohen is under investigation for bank fraud and campaign finance violations, and while that case is separate from Robert Mueller’s investigation into Russian involvement in the 2016 presidential election, many have wondered if Cohen will be tempted to help Mueller in exchange for a little leniency on his own legal troubles. The New York Times’ Maggie Haberman, one of the country’s foremost Trump whisperers, said on CNN that Cohen could end up having to choose between “his life or the president’s.”

But the key question about somebody like Cohen is not only “will he flip” but also “should we trust him if he does?” A Cohen flip would be a big red flag to researchers who study what’s known as “accomplice witnesses” — people who agree to testify against former colleagues and receive, in return, lighter sentences for their own, related, crimes. These kinds of witnesses aren’t treated with enough scrutiny by juries, experts said, and the use of accomplice witnesses and other informants by prosecutors is largely unregulated and undocumented. That’s led some experts to be suspicious about any case that hinges on testimony from someone who is incentivized to talk.

Now, their skepticism is about informants, generally, and doesn’t have anything to do with Cohen or the Mueller investigation specifically. Moreover, incentivized informant testimony — both from accomplice witnesses and from “jailhouse informants” who pass on information gleaned from cell mates — isn’t inherently bad, said Jeffrey Neuschatz, professor of psychology at the University of Alabama in Huntsville. Nobody knows the rates at which they provide inaccurate information (although we do know that humans are willing to alter their behavior in big ways for even small incentives). And both law enforcement and prosecutors say these kinds of witnesses are sometimes necessary to prove a case — especially ones involving complex criminal enterprises where it might be easy to catch a low-level perpetrator and much harder to catch his boss’ boss.

But what we do know is that, when researchers study situations where people went to prison for crimes they did not commit, informant testimony was one of the four major factors contributing to those convictions.

Informants can be a key factor in wrongful convictions Types of evidence involved in the 330 cases exonerated by DNA evidence in the U.S. as of 2015 Type of Evidence No. of Cases Share of Cases Eyewitness misidentification 236 72% – – Poor-quality forensic evidence 234 71 – – Incentivized informants 80 24 – – False confessions 68 21 – – Most cases involved more than one type of evidence Source: Cambridge University Press

For instance, out of the 330 people exonerated by DNA evidence as of 2015, 24 percent of those convictions involved informant testimony, according to research by University of Virginia law professor Brandon Garrett. An earlier study from the Northwestern University School of Law’s Center on Wrongful Convictions, which focused just on capital cases, turned up even higher rates: Of the 111 death row inmates exonerated between the reinstatement of the death penalty in 1976 and 2004, 45.9 percent of their cases involved informant testimony. According to both Garrett and the National Registry of Exonerations, the use of incentivized informants seems to be more common in capital cases than it is when the stakes are lower.

In that way, incentivized informants are similar to three other major issues in the criminal justice system that have also been shown to heavily contribute to wrongful convictions: eyewitness misidentification, false or coerced confessions and flawed forensic science. But while those issues have received widespread attention in recent years from the media, scientists and legal reformers, the problems in incentivized witness testimony have largely flown under the radar. In a 2016 American Criminal Law Review article, Yeshiva University law professor Jessica Roth wrote that no one has any idea how frequently incentivized testimony is used and juries don’t always know when the testimony they are seeing was incentivized. There are no federal requirements that it must be backed up with corroborating evidence, no judicial tests for how it should be used and balanced against civil liberties (unlike, say, the famous Miranda rights that regulate confessions), and no federal investigations or research commissions that have been convened to drive reform.

The inherent risks and lack of oversight are enough that even a former prosecutor like Daniel Blinka, professor of law at Marquette University, said incentivized informants should be a last resort in court — particularly because there’s an inverse relationship between the kinds of cases where these informants are used and the availability of corroborating evidence. “If I have a mountain of corroboration already, I don’t need to give anyone a deal,” he said.

The use (or misuse) of informants has huge stakes. When informants do testify, research suggests that their words could have a significant effect on jurors’ behavior. Neuschatz and Butler University psychology instructor Stacy Wetmore found that incentivized testimony makes mock jurors more likely to convict, even when they were explicitly told by an expert witness that such testimony is unreliable. In a paper soon-to-be-published in the “Journal of Police and Criminal Psychology,” Neuschatz even found that incentivized testimony can make people distrust their own eyes. After watching a video of a crime and choosing the perpetrator out of a lineup, participants were told who a jailhouse informant had fingered for the crime. Of the people who picked a different perp, 80 percent changed their story to match the informants’. Regardless of whether we should believe people who flip, we do.

The Mueller investigation doesn’t involve a jury, but Neuschatz said incentivized testimony can shape the direction any investigation takes. In addition, some of the reforms suggested by experts like Neuschatz, Blinka, Wetmore and Roth would apply to Mueller’s work. Requiring incentivized testimony to be reviewed in a reliability hearing before a judge, for instance, or requiring prosecutor’s offices to adopt formal policies governing when they will and won’t use incentivized sources and how incentives can and can’t be offered. Even simply increasing transparency by requiring that all incentivized testimony be recorded — every interview, not just the final one — would help, according to both Roth and Blinka: Informants are often given multiple attempts at telling their story, and can sometimes change it to fit what prosecutors want to hear. Until reforms happen, Blinka said, we’re often left with little choice but to trust people we shouldn’t and hope justice is served even if the details may be tainted.

It’s still unclear what all this means for Cohen, Mueller and Trump. But if Cohen does flip, it’s worth thinking critically about his motivations — and your own in believing him.