Derek Chauvin's defense attorney made little headway with witnesses William Smock, an emergency medicine physician with specialized training in forensic medicine, and Daniel Isenschmid, a forensic toxicologist, on Thursday afternoon.

Both experts agreed with much of what had been said by pulmonary specialist Martin Tobin earlier in the day in the murder trial of Chauvin, the former Minneapolis police officer who is charged with murder and manslaughter in the death of George Floyd.

Smock, a surgeon with the Louisville Metro Police Department in Kentucky, told the court that Floyd died because of a lack of oxygen in his body, which jurors took great interest in, according to reporters in the courtroom.

"Mr. Floyd died from positional asphyxia," Smock said, watching as most of the jury wrote in their notepads. "It is a fancy way of saying he died because he had no oxygen left in his body."

"When the body is deprived of oxygen, in this case from his chest pressure and back, he gradually succumbed to lower and lower levels of oxygen until it was gone and he died."

His statement went against arguments by the defense, which has suggested that Floyd's death could be blamed on the drug fentanyl, which he was found to have consumed at some point before he died.

He dismissed the idea. "He's breathing. He's talking. He's not snoring. He's saying, 'Please, please get off of me, I can't breathe.' That is not a fentanyl overdose. That's someone begging to breathe," he said.

Low levels of fentanyl, as well as methamphetamine, were found in Floyd's system, forensic toxicologist Isenschmid said. But he dismissed the defense's theory that either played a key role in Floyd's death.

Isenschmid, who works with Pennsylvania-based NMS Labs, told the court that the amounts of the two substances in Floyd's system after his death were lower than the mean of those found in DUI cases and fatal fentanyl overdose analyses performed by the lab.

He added that the quantity of methamphetamine found in Floyd's blood and urine would not have been sufficient to cause intoxication.

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