Chauvin kept knee on neck minutes after Floyd drew last breath, expert says

MINNEAPOLIS — A medical expert testified Thursday that George Floyd died from a lack of oxygen as Derek Chauvin, a now-fired Minneapolis police officer, knelt on Floyd’s neck and then held that position for more than three minutes after Floyd drew his last breath.

Dr. Martin Tobin, a Chicago physician who has specialized in respiratory and critical care medicine for decades, said he has reviewed much of the evidence and concluded that “Floyd died from a low level of oxygen. This caused damage to his brain that we see, and it also caused a (pulseless electrical activity) arrhythmia that caused his heart to stop.”

Cause of death has provided a sharp divide between the state and the defense. The prosecution is saying Floyd died from a lack of oxygen, while defense attorney Eric Nelson has argued that Floyd died of a cardiac arrest, illicit drug use and other factors.

The heavy dose of expert medical testimony filled the day until adjournment later than usual Thursday. The second week of testimony resumes Friday morning.

During the afternoon, jurors heard from a forensic toxicologist at NMS Labs, which tested Flood’s blood for illicit drug use and found the presence of fentanyl and methamphetamine.

David Isenschmid said that while fentanyl was found in Floyd’s blood, so was norfentanyl, which is metabolized fentanyl. Overdose victims who die rarely have norfentanyl in their blood, he said.

He testified that Floyd’s ratio of fentanyl to norfentanyl was 1.96 nanograms per milliliter. This is compared to the average ratio of 9.05 ng/ml in postmortem cases and 3.2 ng/ml in driving under the influence cases of people who survive.

Floyd’s level of methamphetamine was even lower compared to a sample of driving under the influence meth cases.

“Does this show Mr. Floyd was below the average and even below the median in DUI cases?” prosecutor Erin Eldridge asked. “Yes,” he said.

The next witness, the police surgeon of the Louisville Police Department, reviewed videos from Floyd’s arrest and other case records and also concluded that he died from a lack of oxygen and not from a fentanyl overdose. Much of what Dr. Bill Smock testified to supported Tobin’s conclusions about Floyd’s deteriorating condition and movements in his effort to keep breathing.

Smock, who regularly responds to crime scenes and emergency rooms, said that people who overdose on fentanyl become among other things sleepy, snore, have constricted pupils and their breathing rate falls.

Smock said Floyd was not snoring, had dilated pupils, and talking and saying “I can’t breathe.”

The doctor said “that is not a fentanyl overdose. That is someone begging to breathe.”

Smock said Floyd also showed no signs at the scene of a diagnosis called excitable delirium, which someone afflicted grows extremely hot, is moving about rapidly and exhibits superhuman strength. Again, according to Smock, Floyd showed none of the many symptoms of this malady, which one of the officers raised at Floyd’s arrest.

He also addressed the need for CPR, “way before it was. As soon as Mr. Floyd was unconscious, he should have been rolled over. ... When they can’t find a pulse, CPR should have been started.”

Many of Nelson’s questions for Smock centered on various health conditions that Floyd was known to have, an area the defense is asserting had a role in his death.

Smock agreed that Floyd had cardiovascular disease, a severe blockage in an artery, high blood pressure, as well as fentanyl and methamphetamine in his system. He also agreed that struggling with police can put stress on the heart.

As he did earlier this week, Nelson raised the prospect of Floyd being deceptive early on when he was saying he couldn’t breathe when “no one was on his back” while in the squad car. Smock agreed with Nelson’s account of what Floyd said and when.

Jurors paid close attention to Tobin’s testimony from start to finish, watching every video, chart or illustration, listening closely to his testimony, and taking notes at specific points. Tobin spoke directly to the jury most of the time, loosening his tie and unbuttoning his top button to demonstrate parts of the neck. In some cases, jurors followed his lead, but Judge Peter Cahill told them they didn’t have to do so.

Using “precise science,” Tobin said Floyd lapsed into unconsciousness shortly before 8:25 p.m. on May 25 as his oxygen levels plummeted.

After Floyd’s breathing ceased, the doctor said that Chauvin’s “knee remained on the neck for another 3 minutes and 27 seconds.”

Virtually all of the jurors took notes after that calculation.

Tobin also noted that one video showed then-officer J. Alexander Kueng checking Floyd for a pulse and saying that he didn’t find one. From that moment, the doctor said he determined that Chauvin’s knee remained on Floyd for another 2 minutes and 44 seconds.