The First Circuit Court of Appeals in Boston issued an opinion Friday reversing Dzhokhar Tsarnaev's death sentence in the Boston Marathon Bombing case. WGBH Morning Edition Host Joe Mathieu spoke with Northeastern University law professor and WGBH News legal analyst Daniel Medwed about the reversal. The transcript below has been edited for clarity.

Joe Mathieu: You've been following this case for years. In fact, people might remember you first became involved with WGBH News during our coverage in 2015. So your reaction — were you surprised? Did people see this coming?

Daniel Medwed: Frankly, I wasn't surprised, and here's why. Appellate courts tend to scrutinize death penalty trials exceptionally carefully. If you're going to have the ultimate punishment — death — you need to have something approximating the ultimate process. And given the notoriety of this crime, the high profile nature [and] the ample pretrial publicity, Judge O'Toole really had to dot every "i" and cross every "t" to ensure that the trial was fair. And as the First Circuit found, this trial was lacking in some key respects.

Mathieu: So let's talk about the "why" here. I know there was a lot of talk about whether the judge should move the trial out of Boston, for instance. What did the First Circuit cite specifically as grounds?

Medwed: Well, interestingly, the First Circuit didn't cite that change of venue motion as a basis for reversing the conviction. Trial judges receive a lot of leeway on those types of rulings. They're typically only reversed if it's found they abused their discretion, and here Judge O'Toole didn't abuse his discretion, he weighed the pros and cons of keeping the trial in Boston and came down on the side of keeping it here. However, the First Circuit did rely on two other purported errors to justify reversing the case. First, jury selection. It found that Judge O'Toole should have engaged in a much more thorough and robust questioning process of prospective jurors and allowed defense lawyers to dig more deeply into content-specific questions about what jurors specifically might have heard, read or watched with respect to media coverage of the case. There's a precedent in the First Circuit called the Patriarca decision. It involved an infamous mafia boss. And it stands for the proposition that with high-profile defendants like this, where there's a lot of pretrial publicity, trial judges have to do much more than is the typical case to make sure that the jury isn't biased. Here, despite some diligent efforts by the trial judge, he simply didn't do quite enough.

The second issue that the First Circuit cited was that Dzhokhar Tsarnaev was deprived of the chance to fully develop the argument that his late brother, Tamerlan, was the driving force in the bombing and that Dzhokhar was more of a sidekick. This was crucial what's called mitigation evidence, an attempt by the defense to convince the jury to spare his life. And the judge didn't allow Dzhokhar to introduce evidence that Tamerlan had perpetrated a triple homicide in Waltham, an unrelated crime to develop that argument. So those were really the two reasons for the reversal.

Mathieu: One of the immediate things you heard was the impact. We heard from the mayor on this, Daniel, the impact this would have emotionally on the victims [and] on family members, if they had to go through an appeal [and] go through a trial all over again. What are the grounds here in terms of federal prosecutors and their right to appeal?

Medwed: Well, I think the prosecutors have two avenues to pursue to maybe challenge this decision. For one thing, they could ask the full circuit court, the First Circuit, to hear this case, not just the three judges who issued Friday's decision. It's called en banc review, a fancy French term. But not only is en banc review very rare — it's rarely granted — but I'm not sure it's even possible here. The rules of appellate procedure provide that a majority of the active duty judges on the particular circuit must vote for en banc review. And by happenstance, there are only six active duty judges in the First Circuit. We have four judges who are semi-retired on senior status. And since three of those judges signed on to Friday's decision and probably won't vote to reconsider their own work, I don't see how you're going to get a majority here. More notably, the prosecution has 90 days to seek review from the U.S. Supreme Court, to file what's called a writ of certiorari. And I think they'll probably do that. It's always a long shot, statistically, to get the Supreme Court to take your case, but there really is a strong possibility that prosecutors will pursue that.

Mathieu: So let's assume the First Circuit decision stands, Daniel. Does he get a completely new trial? Is it just new sentencing? And if that's the case, would it be for some or all of the crimes? How does all that work?

Medwed: Yeah, it is confusing. Here's the upshot. Basically, there are two trials embedded in a death penalty case. The first one is the guilt phase. The second one is known as the penalty or sentencing phase. Both trials occur in front of the same jury. At Tsarnaev's guilt phase trial back in 2015, the jury convicted him on 30 different counts. Then at the sentencing phase, it imposed death sentences on six of those 30 counts. The consequence of this First Circuit decision is basically just to reopen the sentence for the six death penalty counts. It's not a question of whether he'll be found guilty or innocent — that question has been resolved — it's just a question of whether he will get life or death. As for the remaining 24 counts, three of them were actually tossed in Friday's decision for technical reasons that I won't really go into. But the 21 remaining convictions remain intact, including many, many life sentences. So Tsarnaev isn't going anywhere. He's going to spend the rest of his life in a horrible supermax facility in Florence, Colorado. The only real question is whether he'll face a new death penalty trial on those six counts.

Mathieu: We're out of time, Daniel, but do you think that will happen?

Medwed: I think President Trump and Attorney General Barr, maybe in collaboration with our local U.S. attorney's office, may seek a new death penalty trial. But depending on the outcome of this November's presidential election, we'll have to see whether that actually occurs in 2021.