Jonathan Allen
Minneapolis - A critical care doctor called as a prosecution witness in Derek Chauvin's murder trial testified on Thursday that George Floyd died from a lack of oxygen caused by being handcuffed face down in the street with the former Minneapolis police officer's knee on his neck.
"Mr. Floyd died from a low level of oxygen," Dr. Martin Tobin, who treats patients in a Chicago hospital's intensive care unit, told the jury as the prosecution sought to undermine the argument by Chauvin's defence that Floyd, a 46-year-old black man, died of a drug overdose in the May 2020 arrest.
Chauvin, who is white, has pleaded not guilty to murder and manslaughter charges. Video of the arrest, widely viewed on social media, showed Chauvin pinning Floyd's neck to the ground with his knees for more than nine minutes as Floyd begged for his life, repeatedly gasping: "I can't breathe."
The way that Chauvin and other officers pushed Floyd into the street as they arrested him was like putting the left side of his body "in a vice," Tobin testified. Tobin appeared to confirm the findings of the county medical examiner, who ruled Floyd's death a homicide caused by police restraint.
Floyd's death prompted protests against racism and police brutality in many cities across the United States and around the world.
Here are important moments from the ninth day of witness testimony:
DR. MARTIN TOBIN, EXPERT IN THE RESPIRATORY SYSTEM
After giving the jury a brief overview of how oxygen enters the body through air sacs deep in the lungs, Tobin said the way police restrained Floyd meant he could not take in enough oxygen leading to his heart to stop beating, which he said could be described as asphyxia.
"The cause of the low level of oxygen was shallow breathing," Tobin said.
This resulted from a combination of forces applied by police, including placing Floyd prone on the street, handcuffing his hands behind his back and the officer kneeling on his back and neck.
Tobin unbuttoned his shirt collar at one point and asked jurors to do the same as he felt his neck, describing how Chauvin's knee compressed the delicate tissue of the hypopharynx, blocking that part of the respiratory system in the lower part of the throat.
Tobin calculated that at times Chauvin was exerting 91.5 pounds (41.5 kg) of downward pressure on Floyd's neck.
"All of those forces are going to result in the low tidal volume, which gives you the shallow breaths that we saw here, and so the air will not be able to reach those air sacs," Tobin said.
Chauvin and the three other officers were attempting to arrest Floyd on suspicion of using a fake $20 bill to buy cigarettes at a food store. They were fired the following day.
Tobin discussed frames from the video that he said showed Floyd trying to push his chest up from the street using his fingers and his face as leverage as he struggled for breath. The way Chauvin and another officer, Alex Kueng, manipulated the handcuffs also limited Floyd's breathing, he testified.
"They're pushing the handcuffs into his back and pushing them high, then on the other side you have the street. The street is playing the crucial part," Tobin said. "It's like the left side is in a vice."
Kueng and two other officers are set to face a trial later in the year on charges of aiding and abetting Chauvin in killing Floyd.
Tobin told the jury he declined to take an offered fee from the Minnesota attorney general's office in part because it was his first time testifying as an expert witness in a trial.
In introducing Tobin, prosecutor Jerry Blackwell held up the 1,500-page textbook "Principles and Practice of Mechanical Ventilation" written by Tobin, and he agreed when Blackwell asked if the medical journal Lancet had called it the "bible" on the topic.