Two medical doctors and a forensic toxicologist took the witness stand in Derek Chauvin's murder trial in the death of George Floyd and likely causes of either suffocation, or drug use, ABC and NBC News reported Friday.

Dr. Martin Tobin, a physician and world renowned expert on breathing, took the jury Thursday through the repercussions of the officers' excessive use of force that, he testified, slowly suffocated Floyd.

Floyd was held facedown and handcuffed while officers cranked his arms up against his body, putting pressure against his chest, court records show. Tobin said Chauvin pinned Floyd's neck with his left knee while his right was on Floyd's back and side, compressing Floyd's lungs even more.

"A healthy person subjected to what Mr. Floyd was subjected to would have died as a result," USA Today quoted Tobin as telling the jurors.

Such use of force potentially undercut the defense's argument that Floyd died from a combination of his struggle with officers, health conditions and drugs, Tobin said.

Eric Nelson, Chauvin's lawyer, attempted to obfuscate Tobin's testimony, seemingly to confuse jurors. The defense argued that Floyd's drug use and existing health issues were what killed him.

"Mr. Floyd died from positional asphyxia, which is a fancy way of saying he died because he had no oxygen," Bill Smock, a forensic-medicine expert who works as a surgeon for the Louisville Metro Police Department, said in remarks quoted by The Wall Street Journal.

According to Smock, when the body is deprived of oxygen, in this case from the pressure on his chest and back, the person gradually succumbs to dropping levels of oxygen until it is gone and the person dies.

Dr. Daniel Isenschmid, a forensic pathologist for NMS Laboratory in Pennsylvania, testified the type of fentanyl found in Floyd's system is not normally found in fatal overdose victims, indicating that Floyd did not overdose.

The level of fentanyl found in Floyd's system was lower compared to levels found in 94% of DUI cases, Isenschmid said.

The testimony of medical experts is expected to be crucial in the trial of Chauvin, who is charged with second- and third-degree murder and second-degree manslaughter of the 46-year-old Black man, Floyd.