The new Hulu docuseries “The Girl From Plainville” dramatizes the case of Michelle Carter, a teen girl from Massachusetts who was convicted of crimes for encouraging her boyfriend, Conrad Roy, to commit suicide by carbon monoxide poisoning. The trial raised questions about the different categories of homicide liability and what might prompt prosecutors to charge a crime as murder as opposed to manslaughter or criminally negligent homicide. Daniel Medwed, GBH News legal analyst and Northeastern University law professor, joined GBH’s Morning Edition hosts Paris Alston and Jeremy Siegel to talk about the legal framework for homicide. This transcript has been edited for clarity and length.

Jeremy Siegel: Daniel, I think a lot of people, myself included, are confused about the terminology in this area — the difference between homicide, murder, manslaughter, so on. Set the table for us by telling us about the legal definition of the first one, murder.

Daniel Medwed: Sure. I'll start with murder, and I agree with you, the terminology is confusing and a lot of people conflate the various terms. So first of all, the phrase homicide really is an umbrella concept that covers the full range of crimes that could apply when someone dies in an unnatural way. Second, I'd like to think of homicide liability in terms of an elevator. At the top floor, you have the highest categories; on the bottom floor, the lowest category. So let's start with murder, Jeremy, as you suggested. So at the very top of the elevator, you have what's often called first-degree murder, which is when you kill someone intentionally, plus, there's some aggravating factor. Maybe you've used a weapon of mass destruction, or maybe you've acted with premeditation and deliberation. And in 27 states, certain first-degree murder charges could result in the death penalty. Massachusetts is not one of those states.

Just below first-degree murder, we have second degree murder, and this is just straightforward generic murder. It's when you kill someone intentionally, you fire a gun trying to kill them. But you have done so without an aggravating factor. It's not premeditated. It's not deliberate. You've just acted consciously on purpose. So those are the two chief categories of murder.

Paris Alston: OK, Daniel, so you've explained murder. What's meant by manslaughter then?

Medwed: Manslaughter is just below those two levels of murder, and there are, in turn, two basic types of manslaughter. So on the one hand, you have what's called voluntary manslaughter. That's when you kill someone intentionally. It would otherwise be murder in the second degree, but you do so because you were in the heat of passion because you were provoked. Say you've seen your spouse in the arms of their lover and it causes your blood to boil and you do kill one of them. We don't excuse that behavior. It's still abhorrent behavior, but as a concession to the frailty of the human condition, we treat it as voluntary manslaughter, a notch below second-degree murder.

And on the other hand, there's something called involuntary manslaughter. That's when you don't kill someone intentionally, but you do so recklessly. That is, you consciously disregard a substantial and unjustifiable risk of death, and you act in a way that's a vast departure from what we'd expect a reasonable person would do. A lot of extreme drunk driving cases fall into this category of involuntary manslaughter when it results in a fatality.

Siegel: So, Daniel, let's talk about this case that's been made into a Hulu series, the case of Michelle Carter. Where does it fit into that web of different distinctions that you just described?

Medwed: So the place where it fits is in that final category I mentioned, reckless manslaughter. At least that's how the prosecutors charged it. Their theory of the case was that essentially she [Carter] consciously disregarded a substantial risk that by goading her boyfriend, Conrad Roy, whom she knew to be experiencing suicidal ideation, goading him to commit suicide, providing him with a roadmap to how to die by carbon monoxide poisoning, that that was a gross departure from what we'd expect of a reasonable person. And therefore, it was a form of reckless manslaughter. That's where it fits in.

Now, it's a controversial case for a number of reasons. There's an argument that it was her words, not her actions, that led to his death, and also that he made that autonomous decision to die. So there's an argument that maybe she wasn't the direct cause of his death. So there were a lot of sort of legal problems in the case, but the actual homicide theory was involuntary manslaughter.

Alston: And Daniel, what do prosecutors take into account in deciding whether to charge a homicide at one of these particular levels?

Medwed: That's a really interesting question — they take a lot of different things into account. First and foremost, there are certain legal and ethical rules that require prosecutors to proceed only if they have what's called probable cause of guilt. So they can't just take a flier. There has to be some basis in the evidence, some probability, that the person is in fact guilty and then at trial you're only convicted, of course, if the evidence proves your guilt beyond reasonable doubt. So that's the first sort of threshold.

A second consideration relates to punishment theory. A prosecutor might look at this case and they'll think, how blameworthy is this person? Are they deserving of a very serious charge or a less serious charge? What about the potential deterrent effect? If we file a charge, A, will it deter this person or other actors from going down the same road and committing the same crime? What is the message we're sending to the community? And third, and finally, and this is a reality of prosecutorial work. There's sort of the political machinations involved. Prosecutors like to secure convictions — whether that's a good thing or a bad thing we can discuss when we have more time. But they want to make sure that they actually can secure a conviction rather than just proceeding in sort of a witch hunt. So those are some of the different factors involved.

"It's a controversial case for a number of reasons."
-Daniel Medwed, GBH News Legal Analyst

Siegel: While we have you explaining all of this really clearly, I wanted to ask about a concept called felony murder, which is something that I've heard in the news or television series, but it's confusing. Where does that concept, felony murder, fit into this hierarchy of homicide charges that you've described?

Medwed: Thanks for bringing me back to murder. It goes into those top floors in first-degree and second-degree murder. And the basic idea, at least in Ye Olde England, was if you commit a felony and someone dies, even if it's inexplicable, inadvertent, that's murder. You commit a burglary and the resident has a heart attack and dies, in Ye Ole England, that's murder. And in many states, that broad or pure felony murder rule was pretty popular.

The recent trend, and it's also in Massachusetts, is to get rid of that pure felony murder doctrine and just treat felony murder as a way to raise second-degree murder to first-degree murder. That is, if you kill someone and you have the requisite mental state for murder in the second degree, the fact that it occurred as part of the felony will raise it to murder in the first degree. That's a short answer.