RACHEL MARTIN, HOST:
The trial of a former Minneapolis police officer turns on this question. Can defense lawyers show that George Floyd's death was different than it seemed on video? Derek Chauvin's knee on Floyd's neck last year prompted nationwide demands to reckon with racism. Lawyers for Chauvin have been trying to convince the jury in his murder trial that Floyd died from something else. But medical experts' testimony this week has made that more difficult. NPR's Cheryl Corley has been following the case and joins us now. Cheryl, I understand today Hennepin County's chief medical officer is expected to testify. Other medical experts were on the stand yesterday. What did they say?
CHERYL CORLEY, BYLINE: Well, one of the main witnesses was Dr. Martin Tobin. And he's a national expert on breathing. And prosecutors asked him to review the medical records and videos tied to this case. And Tobin said, in his opinion, Floyd died from shallow breathing, that he just didn't have enough oxygen getting into his lungs. And that damaged his brain and caused his heart to stop.
MARTIN: Did he make the connection? I mean, did he say that the reason that his oxygen flow stopped was the knee on the neck?
CORLEY: Well, that was part of the reason, he said. He said there were four main factors. The knee was one, another knee on the back, Floyd's body position - he was prone on his chest in the street - and finally, how officers pushed on the handcuffs on Floyd's wrist.
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MARTIN TOBIN: Forcing his left wrist up into his chest, forcing it in tight against his chest, forcing it higher up. And you have to keep in mind that the opposite side of this is the street. So he was being squashed between the two sides.
CORLEY: And Tobin explained many of the technical details he was talking about by using detailed photos and graphs that he created himself to support his contention.
MARTIN: What kind of impact did this have on the jury, this testimony?
CORLEY: Well, according to the pool reporters in the courtroom, the jurors were very engaged. Tobin spoke directly to them, kind of like he was in a classroom. And he talked about the mechanics of breathing. And he asked them to follow along to kind of put their hands on their necks. And many of the jurors did that. But after a while, defense attorney Eric Nelson objected. And Judge Peter Cahill stepped in.
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PETER CAHILL: Members of the jury, the witnesses ask you to do certain things. These are not required. You may do them. And he should phrase it more in terms of if you were to do that. And if you wish to do it, that is your choice.
MARTIN: So Cheryl, these medical experts are there saying Floyd died because of lack of oxygen and the lack of oxygen being caused in part by Chauvin's knee on his neck. How did Chauvin's defense lawyers try to counter that?
CORLEY: Well, Eric Nelson, the defense attorney, returned to his theory that it was drugs that affected Floyd's oxygen levels and caused his subsequent death. And he asked Dr. Tobin to consider a hypothetical since an autopsy had found fentanyl and methamphetamine in Floyd's body.
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ERIC NELSON: Is it fair to say that you would expect a peak fentanyl respiratory depression within about five minutes?
TOBIN: Right. I mean, obviously, it would depend on how much of it was ingested.
CORLEY: But Tobin added that it wasn't drugs but bodyweight on Floyd's neck and back that stopped the flow of oxygen to his brain and caused his death. And another witness, a Louisville police department surgeon, also testified that Floyd died from a lack of oxygen and not a drug overdose, as the defense argues.
MARTIN: And I mentioned earlier, Hennepin County chief medical examiner will testify today. He conducted Floyd's autopsy. How is that likely to impact the case?
CORLEY: Well, we're going to see what he has to say. He's called Floyd's death a homicide.
MARTIN: All right. NPR's Cheryl Corley. Thank you.
CORLEY: You're welcome. Transcript provided by NPR, Copyright NPR.
