Minneapolis police officer Derek Chauvin has been charged in the killing of George Floyd, but the story continues to evolve. WGBH Morning Edition host Joe Mathieu spoke with Northeastern University law professor and WGBH News legal analyst Daniel Medwed to learn more about the criminal case against Chauvin. The transcript has been edited for clarity.

Joe Mathieu: One of the major headlines yesterday, Daniel, was a second independent autopsy on George Floyd finding his death was a homicide and says his heart stopped beating while police restrained him and compressed his neck, and they continued to sit on his body after he died. Floyd's family attorney says this should result in charges being upgraded to first degree murder.

Daniel Medwed: Well, that's an interesting point here because Chauvin has been charged with third degree murder and second degree manslaughter, and there's a compelling argument that maybe those charges are too lenient. Yesterday's news not only from the independent autopsy that Benjamin Crump, the family lawyer, has talked about, but also the final report from the Hennepin County medical examiner, both of those autopsies support the idea that Chauvin caused Mr. Floyds death. And what will probably happen at trial, regardless of the specific charges that go forward, is that there'll be a battle of the experts where the prosecution is going to have to prove beyond a reasonable doubt that Chauvin caused Floyd's death, while the defense is going to point to some other factors to try to create reasonable doubt about that.

Mathieu: So your point is that if this changes anything, it'll be during trial. This call for prosecutors to go for a first degree murder charge — to upgrade charges now — would not be considered normal procedure?

Mdewed: Well, it's possible that they could refile the charges and upgrade them from third degree, perhaps to second degree. I think first degree murder might be a reach for prosecutors, and here's why. Under Minnesota law, you do have to prove premeditation and deliberation. That's possible here, but quite difficult. I think a stronger theory for the prosecutors, and one that I think they should have pursued, is second degree murder, which carries a much higher sentence than the 25 years that's eligible under the third degree murder charge. The theory for second degree murder is that Chauvin intended to kill Floyd — that over the course of those alarming eight minutes, he developed the conscious objective to kill and that second degree murder is warranted. So it's possible, though I'm not entirely confident that the Hennepin County attorney could reconsider and refile higher charges.

Mathieu: Daniel, there've been a lot of reports about previous misconduct involving this officer — other violent encounters with civilians. I'm guessing that could be used as very important evidence here.

Medwed: Absolutely. The prosecution would love to get that evidence in, but here's the rub. Historically, it's very difficult to get in other bad act evidence in criminal cases based on something known as the character propensity ban. The idea is if the jury hears about past actions like this about Chauvin, it might overvalue that evidence, think that Chauvin acted in conformity with his bad character trait during the Floyd killing and basically convict him based on his character, not on the four corners of what they see on that video and the evidence in the case. However, prosecutors could argue that you can go around that ban by showing that Chauvin had a very idiosyncratic pattern here, a pattern of violence against civilians, especially people of color, that it rose to the level of being a modus operandi, his method of operation, and basically, it's his signature; the jury should hear about it. So there's going to be a big preliminary battle in court about that bad act evidence.