Sometimes, defense lawyers get it wrong. WGBH Morning Edition Host Joe Mathieu spoke with Northeastern University law professor and WGBH News legal analyst Daniel Medwed about how a defense lawyer's performance can lead to a wrongful conviction. This transcript has been edited for clarity.

Joe Mathieu: Let's start with the big picture here, as this apparently hits close to home for you. How do defense lawyers tend to play a role in contributing to wrongful convictions?

Daniel Medwed: Well, in a litany of different ways, both in and out of court. For the most part, I often say this: cases are won or lost based on pre-trial preparation and investigation. And due to a lack of resources and sometimes training, defense lawyers don't always do a super stellar job in that regard.

So here's an example from my own cases. I handled a case involving a man named Steven on appeal. He'd been convicted of robbery; he allegedly stole some money from a store front restaurant in Long Island. While he's sitting in the county lockup, he's reading the local newspaper when he comes across an article about another man named Anthony who'd pleaded guilty to six factually analogous storefront robberies in Long Island during this time frame. Steven, claiming to be innocent, picks up the phone and he calls his defense lawyer, a guy named Barry. He said, "Barry, investigate this! I'm innocent. This guy Anthony probably did it." Barry said, "Let's see how it plays out at trial. Let's just sit tight." Well, it didn't play well for Steven. He was convicted of robbery and sentenced to 11 years in prison.

Mathieu: Wow. What happened?

Medwed: He wrote to me while his case was on appeal. I was helping to run an innocence project at Brooklyn Law School at the time, and he asked me to take on his case. So my students and I started investigating it, and we found a lot of evidence that this other guy Anthony had in fact committed this particular robbery. We filed a bunch of state filings and we lost. It took us six years before he made it to federal court and the federal judge issued a writ of habeas corpus, releasing Steven on the grounds of ineffective assistance of his trial attorney for failing to investigate Antony's culpability.

Mathieu: I love this first-person stuff, Daniel. So what does it take to overturn a case on the grounds of incompetency or ineffectiveness by the defense lawyer?

Medwed: Well, the current test derives from a famous 1984 case called Strickland v. Washington, which set up a two-part test. First, you have to show that the defense lawyer was deficient — they did something wrong that was actually inadequate. Second, you have to show that because of that inadequacy, you had a bad result. In other words, but for the misstep would the result have been different? Would you have been acquitted, or been convicted of a lesser charge? So it's fairly easy to show deficiency: my lawyer didn't investigate the case, my lawyer fell asleep at trial. But it's a lot harder to prove that that deficiency made a difference in the outcome.

Mathieu: You mentioned the lack of resources and training earlier. Is that why defense attorneys might engage in sub-par lawyering?

Medwed: Well, that's a big part of it. As we talk about the criminal justice system, we're always talking about dollars and cents. Public defenders are notoriously overworked and underpaid, and as devoted as they are, they sometimes just can't do their job as well as they'd like because of a lack of resources. So another war story.

When I was a public defender at the Legal Aid Society of New York City, I was in the criminal appeals bureau with dozens and dozens of lawyers. We could only afford a half-time private investigator, whereas the prosecutors could rely on the best investigators in the world for free: the New York Police Department. But get this: the half-time investigator couldn't drive. He didn't know how to drive. And in New York, that's actually an impediment because the subway doesn't go to huge swaths of Brooklyn, Queens, Staten Island and the Bronx. So we were not only paying him half-time, but then we had to reimburse him for all these taxi receipts. I learned my lesson later when I was doing the innocence clinic that my students and I should just do it on our own.