Plea bargains are common in the justice system — approximately 90 percent of criminal defendants choose to plead guilty rather than go to trial. WGBH News' Morning Edition Host Joe Mathieu spoke with Northeastern University law professor and WGBH Legal Analyst Daniel Medwed to discuss the pros and cons of a plea bargain. The transcript below has been edited for clarity.

Joe Mathieu: So let's start with the nuts and bolts here, and how a plea bargain actually works.

Daniel Medwed: Sure. I'll break it down into informal and formal steps. First, it's the prosecutor's ballgame. They decide whether to offer a plea, when to offer it and what's contained in the plea offer. Sometimes that first plea offer is very enticing to the defendant — maybe to plead guilty to a lesser crime at a fraction of the prison sentence that the defendant would be facing if he were convicted after trial. These negotiations often happen behind the scenes, in courthouse hallways and vestibules, where the prosecutor and the defense lawyer broker this deal. Then eventually it goes to court, where the judge, at least nominally, has review powers. It’s really a pro forma affair, though; the judge doesn't really do much. The defendant shows up in court for what's called a plea allocution, where the defendant has to mention in open court that they're guilty, with an eye toward determining whether or not the plea is being rendered voluntarily.

Mathieu: So why has it become popular, though? You would think more prosecutors and defendants would want to go to trial.

Medwed: Well, that's a really important question, and I think it boils down to efficiency. It's efficient, and sometimes it actually works pretty well. So on the one hand, take the prosecutor. You think somebody is guilty, a plea is a chance to secure a conviction and a punishment without the time, expense and uncertainty of rolling the die at trial and maybe getting an acquittal. And on the other hand, consider the defendant. The defendant has a chance to lock in a sentence that's much more lenient [and] much more benign than what they might be facing if they were convicted at trial. Now that said, it's very flawed. There are [a lot] of problems with the process.

Mathieu: What are the flaws?

Medwed: Well, here are two big ones. First, bargaining only works when people are basically equals — when they have access to similar information and they can negotiate in a strong position. That’s not the case in the criminal justice system, where prosecutors hold all the cards. They have all the evidence about the strength and weakness of the case. And under Supreme Court precedent, prosecutors aren't required to disclose that evidence, let alone evidence that exculpate or is favorable to the defendant, before a plea. Second and more notably, the entire process is inherently coercive. Consider this: you're a defendant who's facing 15 years if you're convicted after trial. The prosecutor comes to you with a plea offer of three years. Even if you're innocent, if you're risk averse, wouldn't you maybe take that deal? So while prosecutors view this process as a plea discount — you get a discount for taking the deal early on — a lot of defendants view it as a trial tax. It's a tax on your constitutional right to go to trial.

Mathieu: That's pretty tough. But assuming pleas are here to stay, can we make them fairer based on everything you just said?

Medwed: Well, that assumption is spot on. Absent a decriminalization movement, our system would collapse under the weight of all these trials, if cases didn't plead out. So it is here to stay. Here are a couple reforms that basically track some of the problems I've identified. First, let's get rid of that information deficit — that information asymmetry for the defendant— and require prosecutors to disclose evidence before a plea, to give the defendant access to more information about the strength and weakness of the case before entering a plea.

Second, we could restrict, or cap, the discrepancy in the plea offer and the post-trial sentencing exposure. Italy already does this. In Italy, prosecutors cannot offer a plea that's less than one-third of the sentence the defendant would be facing after trial, because if it's such a wide gulf, then maybe innocent defendants might be seduced into accepting the deal. Maybe we should follow the Italians. And lastly, judges could engage, or should engage, in a more searching and robust vetting of pleas. They shouldn't just sign off on these cases. Maybe they could ferret out wrongful convictions that way.