A veteran lung doctor testified on Thursday that George Floyd’s death was caused in part by Derek Chauvin’s knees pressing against his neck and back, making it impossible for him to breathe, and that Mr. Floyd showed signs of a brain injury about four minutes before Mr. Chauvin lifted his knee from his neck.
Dr. Martin J. Tobin, a pulmonologist and critical care doctor in Chicago, said in court that the combination of Mr. Chauvin’s pressure, the handcuffs pulling Mr. Floyd’s hands behind his back and Mr. Floyd’s body being pressed against the street had caused him to die “from a low level of oxygen.”
The testimony from Dr. Tobin on the ninth day of the trial of Mr. Chauvin, the former Minneapolis police officer who has been charged with murdering Mr. Floyd, signaled a shift into a new phase in which medical testimony will be crucial. Mr. Chauvin’s lawyer has suggested that Mr. Floyd died from the fentanyl and methamphetamine that were found in his system, but prosecutors argue that Mr. Chauvin had killed him by kneeling on him for more than nine minutes and cutting off his air supply.
Dr. Tobin was adamant that Mr. Chauvin’s actions had caused Mr. Floyd’s death on May 25. He pinpointed the exact moment, in the graphic bystander video of the arrest, in which he said Mr. Floyd had died, noting that his eyes had opened wide and then closed again. At that point, Mr. Chauvin’s knee remained on his neck.
“You can see his eyes — he’s conscious — and then you see that he isn’t,” Dr. Tobin said. “That’s the moment the life goes out of his body.”
The doctor also rejected the defense’s arguments about drugs, saying that videos show Mr. Floyd breathing at a normal rate before he went unconscious, meaning any fentanyl in his system was “not having an effect” on his breathing.
“A healthy person subjected to what Mr. Floyd was subjected to would have died,” Dr. Tobin said.
After analyzing videos of the arrest, Dr. Tobin said he determined that Mr. Chauvin had pressed his left knee on Mr. Floyd’s neck for more than 90 percent of the time that Mr. Floyd was on the ground, and that he had kept his right knee on Mr. Floyd’s back for the majority of the time as well. That pressure, combined with having his hands cuffed behind his back and pushed into the street facedown, had cut off oxygen and caused his heart to stop, Dr. Tobin said.
“He was being squashed between the two sides,” he said.
Mr. Floyd was so desperate for air at one point that he tried to lift himself off the ground by pushing his right knuckle against a police car’s tire, the doctor said.
Dr. Tobin, who works in pulmonology and critical care at Edward Hines Jr. Veterans Affairs Hospital and at Loyola University’s medical school, spoke for more than two hours to jurors. He said he had asked not to be paid when prosecutors asked if he would testify in the case. At several points, he encouraged jurors to feel parts of their own necks to demonstrate what he was saying; most of them followed along.
Dr. Tobin said the factors that cut off Mr. Floyd’s air supply had led to what could be called “asphyxia,” which he said is just another word for oxygen deprivation; a prosecutor told jurors when the trial began that Mr. Floyd had died of asphyxia.
At one point in a video of Mr. Floyd’s arrest, Dr. Tobin noted, Mr. Chauvin’s left foot appeared to rise off the ground, which the doctor said meant that half of Mr. Chauvin’s body weight was pressing on Mr. Floyd’s neck.
After about 4 minutes and 51 seconds, Dr. Tobin said, Mr. Floyd stopped speaking or groaning. After just over 5 minutes, Mr. Floyd appeared to straighten out his legs, which Dr. Tobin said was a signal that Mr. Floyd was having a type of seizure because he had suffered a brain injury from the oxygen deprivation. He said Mr. Chauvin’s knee had stayed on Mr. Floyd’s neck for 3 minutes and 27 seconds after he took his last breath.
The doctor said the handcuffs were also an “extremely important” factor in Mr. Floyd’s death because Mr. Chauvin and another officer had pushed his hands upward and against his back, pressing his chest against the hard street.
“When you’re turned prone and with the knee on the back, now the work that Mr. Floyd has to perform becomes huge,” Dr. Tobin said, adding: “He has to try to lift up the officer’s knee with each breath.”