George Floyd

Expert Witnesses Reinforce the Prosecution's Case That Obstructed Breathing Killed George Floyd

The witnesses rejected the defense's suggestion that Floyd might have died from a drug overdose.


The prosecution in Derek Chauvin's murder trial argues that the former Minneapolis police officer killed George Floyd by pinning him facedown to the pavement for nine and half minutes. In that position, prosecutors say, Floyd could not breathe enough to stay alive. Today expert witnesses reinforced that account, saying the evidence indicates that Floyd—who complained 27 times that he was having trouble breathing—died from lack of oxygen.

Chicago physician Martin Tobin, who specializes in pulmonary and critical care medicine, noted that Floyd, who was arrested on May 25 for using a counterfeit $20 bill to buy cigarettes, was handcuffed behind his back and forced to lie on his stomach, both of which would have made breathing difficult. At the same time, Chauvin had one knee on Floyd's neck and frequently had the other on his arm, pressing against the side of his chest. Officer J. Alexander Kueng, meanwhile, was applying pressure to Floyd's back, and Officer Thomas Lane was holding down his legs. Tobin also noted that video shows Chauvin and Kueng "pushing [the handcuffs] into his back and pushing them high," which would have made it even harder to breathe.

Based on how Chauvin was positioned and taking into account the gear he was wearing, Tobin estimated that he was applying 87 to 91 pounds of weight to Floyd's neck. "We're talking half of his body weight and half of his gear [weight], and all of that is coming down," he said. "It's like the left side is in a vise. It's being pushed in from the street at the bottom, and the way the handcuffs are manipulated…totally interferes with central features of how we breathe."

Chauvin's attorney, Eric Nelson, has suggested that the officers thought Floyd was faking when said, over and over again, that he could not breathe. But Tobin cited other indications of Floyd's respiratory distress: He lifted his left shoulder in an attempt to relieve the pressure on his lungs, for example, and tried to create breathing space by pushing his fingers against the street and a squad car tire.

With his chest against the pavement and the officers pushing on him from above, Floyd "was being squashed between the two sides," Tobin said. "On the left side of his lung, it was almost as if…a surgeon had gone in and removed the lung…There was very little opportunity for him to be able to get any air to move into the left side of his chest." He said the pressure on Floyd's neck also restricted the "air getting into the passageway," with an effect similar to breathing through a straw, which is "enormously difficult."

About five minutes after he was pinned to the street, Floyd "kicked out his leg in an extension form," which Tobin said indicated "brain injury from a low level of oxygen." Floyd lost consciousness around the same time and stopped breathing 23 seconds later. Chauvin's knee "remained on the neck for another 3 minutes and 2 seconds," even after Kueng checked for a pulse and said he could not find one.

"Floyd died from a low level of oxygen," Tobin said. "This caused damage to his brain that we see, and it also caused a PEA [pulseless electrical activity] arrhythmia that caused his heart to stop."

That conclusion is broadly consistent with the results of an independent autopsy commissioned by Floyd's family. Forensic pathologists Michael Baden and Allecia Wilson said Floyd died from "mechanical asphyxia." The autopsy report from the Hennepin County Medical Examiner's Office, by contrast, said nothing about asphyxia, attributing Floyd's death to "cardiopulmonary arrest complicating law enforcement subdual, restraint, and neck compression." Both reports described the manner of death as homicide.

"Cardiopulmonary arrest," of course, means Floyd's heart and lungs stopped functioning, which would describe any death. As Tobin noted, lack of oxygen can cause arrhythmia. But the same use of force that made it hard for Floyd to breathe also could have affected blood flow or heart activity more directly. The respiratory and cardiovascular systems are so intertwined that it may be impossible to conclusively say which failed first.

Does it matter? If "law enforcement subdual, restraint, and neck compression" contributed to the "cardiopulmonary arrest" described in the official autopsy report, that still means the cops killed Floyd, and so does the determination that his death was a homicide.

The defense argues that Floyd "died of a cardiac arrhythmia that occurred as a result of hypertension, his coronary disease, the ingestion of methamphetamine and fentanyl, and the adrenaline flowing through his body, all of which acted to further compromise an already compromised heart." But it strains credulity to suppose that the stress inflicted by Floyd's prolonged prone restraint had nothing to do with "the adrenaline flowing through his body" or the ensuing "cardiac arrhythmia."

Nelson has implicitly conceded that the officers' actions were the but-for cause of Floyd's death. In a pretrial motion, he faulted Kueng and Lane for needlessly escalating the situation by trying to force Floyd into their squad car. "If Kueng and Lane had chosen to de-escalate instead of struggle, Mr. Floyd may have survived," he said. What can that mean except that Floyd died because of the way the cops treated him?

Although video of the arrest plainly shows Chauvin with his knee on Floyd's neck, Nelson maintains that Chauvin actually placed his knee "between the shoulder blades at the base of the neck." Today he noted that no bruising was found on Floyd's neck, which Tobin said is consistent with the steady pressure that Chauvin applied. "When I go to church, I sit on a hard bench," he said. "I don't get bruising on my bottom."

But the exact position of Chauvin's knee, or the way we describe it, does not matter if the issue is the respiratory difficulty caused by keeping Floyd pinned facedown to the ground. Nor does it matter if the issue is the cardiac stress caused by that prolonged prone restraint. Either way, Floyd would have survived this encounter if the cops had handled it differently.

Nelson has suggested that Floyd, who had swallowed black-market "Percocet" tablets containing fentanyl and methamphetamine, might have died from a drug overdose. But judging from the blood test results, that seems quite unlikely. David Isenschmid, a forensic toxicologist who also testified today, said the ratio of fentanyl to the metabolite norfentanyl in Floyd's blood was much lower than what is typically seen in fatal overdose cases.

Tobin also cast doubt on the idea that fentanyl could have killed Floyd. While Floyd was having trouble drawing adequate breaths, he said, his breathing rate was normal, which is inconsistent with the respiratory depression caused by an opioid overdose.

"The cause of the low level of oxygen was shallow breathing," Tobin said. Because of the pressure on his chest, he said, Floyd was taking "small breaths…that weren't able to carry the air through his lungs down to the essential areas of the lungs that get oxygen into the blood and get rid of the carbon dioxide."

Tobin also noted that someone who dies of a fentanyl overdose first lapses into a coma, and that did not happen in Floyd's case. Bill Smock, a physician who specializes in emergency medicine, likewise said Floyd did not exhibit signs of a fentanyl overdose: He was talking, he was not sleepy, and his pupils were not constricted. "That is not a fentanyl overdose," he said. "That is someone begging to breathe."