UPDATE (5:15 p.m.): Dr. Bill Smock, the last witness for the prosecution Thursday in the Derek Chauvin trial, said that in his view George Floyd died as a result of “positional asphyxia,” or “a fancy way of saying” he had no oxygen left in his body.

Smock — a surgeon and forensic medicine expert who worked in a medical examiner’s office and now works at the Louisville Police Department — was called on by the prosecution to go over the 10 signs of “excited delirium,” a disputed condition that Smock said he does not believe applies in Floyd’s death.

Smock said that his analysis of the Floyd footage indicates that he exhibited none of the 10 signs of “excited delirium” prior to his death.

“Zip,” he said.

Normally, at least six of the 10 signs would need to be present to diagnose it.

Probed by the prosecution, Smock delved into the topic of “air hunger,” saying it’s the state of doing whatever it takes to breathe, and adding that Floyd’s pleas of “I can’t breathe” spoke to that state. He held this in contrast to behavior typically observed in overdose cases.

In cross-examination, defense attorney Eric Nelson asked Smock if it’s fair to say he’s not a pathologist. Smock agreed, and said he studied forensic pathology as it applies to living patients. Asked how many autopsies he has performed, he said about 100, but added he’s observed thousands.

Asked if he’s seen anything in Floyd’s autopsy that would indicate an obstructed airway, Smock said he did not. Nelson asked Smock whether, if Derek Chauvin’s knee was at the base of George Floyd’s neck, that would affect his diaphragm. Smock said it wouldn’t.

Nelson asked a few questions about heart issues and the prosecution raised objections. In its redirect, the prosecution came out of the gate asking if there’s any evidence that Floyd died of a heart attack. Smock said, “Absolutely not.” Asked if he believes Floyd died of a fentanyl overdose, or an amphetamine dose, or a combination of the two, Smock said, “No, he did not.”

Cahill then adjourned court for the day at about 5:15 p.m., thanking the jury for “sticking this out” longer than usual for the day.

UPDATE (4 p.m.): Dr. Daniel Isenschmid now takes the stand. He works as a forensic toxicologist at NMS Labs in Horsham, Pennsylvania. State is asking him about findings of drugs in George Floyd’s system.

Isenschmid analyzed George Floyd’s blood collected at Hennepin Healthcare and urine from the autopsy. Isenschmid discussed the levels of certain drugs found in George Floyd’s system, including fentanyl and methamphetamine.

Isenschmid says Floyd’s fentanyl ratio was below the median level in driving under the influence cases. He said caffeine and codeine, which indicates smoking, was found in his system.

Defense cross-examined Isenschmid, focusing primarily on the rate of metabolism of certain substances in humans’ systems. Isenschmid said that different drugs do process through the body at different rates.

The prosecution concludes their questioning and calls up the final witness for Thursday — Dr. Bill Smock, a surgeon and forensic expert from Louisville, Kentucky.

UPDATE (2:20 p.m.): Defense attorney Eric Nelson asks Dr. Martin Tobin if he’s a pathologist. Tobin says no.

Nelson brings up “wooden chest syndrome”, which is a medical condition where fentanyl can create a rigid chest wall for some users. Tobin agrees it would impede the lungs.

Nelson asks Tobin if fentanyl can cause death by low oxygen levels, Tobin answers “Yes, but only in part.”

Tobin excused after follow-up. Court takes a short break.

UPDATE (12:09 p.m.): Dr. Martin Tobin, a lung and breathing expert based out of Chicago, testified that a healthy person would have died if they were restrained as George Floyd was on May 25 — lying prone, in handcuffs and with knees pressing on their neck and back.

The doctor told the court that he could tell by Floyd’s facial expressions “the moment the life goes out of his body.” A slow-motion clip of the widely-seen bystander video was played in court, showing the precise moment to the jurors. Tobin explained that because of his work in an ICU, he’s “very familiar with watching people die, unfortunately.”

According to Tobin, when Floyd gasped his last words — “I can’t breathe” — he still had oxygen in his brain. But shortly thereafter, he suffered a major loss of oxygen, as evidence by a movement of his leg captured on body-worn camera video. “Bottom line is the leg jumps up like that as a result of a fatally low level of oxygen in the brain,” Tobin said.

While Tobin said that it’s true that if “people can speak then they can breathe,” that’s an unreliable motto. “When you can speak you are breathing, but it doesn’t mean you are breathing five seconds later,” he said.

Through multiple slides, the world-renowned doctor explained to the jury how lying prone with pressure on the back can significantly reduce breathing and oxygen reserves in the lungs. He also showed that when restrictions to the airway reach a certain threshold, it becomes a herculean task to breathe.

According to the pool reporter inside the courtroom, the jurors were engaged throughout the two hours of direct examination, with many taking notes and looking attentive, despite its highly technical nature.

Anticipating arguments from the defense, which is trying to argue that Floyd died of an overdose, Tobin noted that Floyd’s respiratory rate was normal during his arrest, saying that if he were under the influence of fentanyl it would have been significantly lower. Tobin even counted Floyd’s breaths from the body-worn camera video in order to explain the point to the jurors.

Additionally, Tobin said that the elevated levels of carbon dioxide recorded in Floyd’s blood were a result of lack of oxygen, not fentanyl. The doctor said that based on the nine minutes between Floyd’s last recorded breath and when paramedics pumped oxygen into his lungs, his carbon dioxide levels are exactly what he’d expect them to be.

The court is now out for a lunch break. After, Eric Nelson, Derek Chauvin’s attorney, will be up to cross examine Tobin.

UPDATE (10:30 a.m.): The first person to take the stand Thursday was Dr. Martin Tobin, a physician in pulmonary critical care and an world-renowned expert in respiratory physiology.

When prosecutor Jerry Blackwell asked the doctor’s opinion on George Floyd’s death, Tobin said that Floyd died from a “low level of oxygen,” which caused damage to Floyd’s brain and an arrhythmia that caused his heart to stop.

“The cause of the low level of oxygen was shallow breathing, shallow breaths that weren’t able to carry the air through his lungs down to the essential area of the lungs that get oxygen to the lungs and get rid of the carbon dioxide,” Tobin said.

Tobin testified that the main forces that led to Floyd’s fatal “shallow breaths” were:

– Floyd lying prone
– Floyd being in handcuffs
– Floyd having a knee on his neck
– and Floyd having a knee on his back/side.

While showing a computer rendering of the arrest to the court, Tobin explained that the handcuffs, combined with Floyd’s placement on the ground, created something of a vice on Floyd’s left side, making it virtually impossible for him to get air into the left side of his chest.

Tobin noted that Floyd was pushing on the pavement and the squad car’s tire with his fingers and knuckles, trying to lift his chest in order to breathe.

“To most people, this doesn’t look terribly significant, but to a physiologist, this is extraordinarily significant,” Tobin said. “Because this tells you he has used up his resources and he is now literally trying to breathe with his fingers and knuckles.”

Tobin explained that during certain moments of the restraint, Chauvin had his knee pressing down directly on Floyd’s hypopharynx, a small but crucial airway. At one point, Chauvin had half of his weight — about 90 pounds — applied directly to Floyd’s neck, as the ex-officer’s foot can be seen lifted off the ground.

MINNEAPOLIS (WCCO) — The ninth day of testimony in the Derek Chauvin trial is set for Thursday, and it’s possible that the state will begin calling medical experts to testify that George Floyd died of asphyxia under the ex-officer’s knee.

Court is expected to resume around 8:30 a.m. with a hearing concerning the possible testimony of Morries Hall, the man who was with Floyd in a vehicle on May 25 before officers arrived at 38th and Chicago. Courteney Ross, Floyd’s girlfriend, testified last week that Hall sold Floyd and her drugs, as recently as a week before Floyd’s death.

In a pretrial hearing on Tuesday, Adrienne Cousins, Hall’s public defender, said that her client would invoke his 5th Amendment right against self-incrimination. She argued that if Hall testifies, he could be charged with third-degree murder in Floyd’s death.

RELATED: Expert Says Chauvin Never Took Knee Off George Floyd’s Neck

Judge Peter Cahill agreed that much of the defense’s questions for Hall would be incriminating. However, he believed that Hall could testify to Floyd’s state in the car before officers arrived outside Cup Foods. The judge instructed Eric Nelson, Chauvin’s attorney, to draft questions for Hall and Counsins to consider by Thursday.

The morning hearing could end with Hall agreeing to testify on the questions provided. However, it could also end with Hall being granted immunity, thereby nullifying the risk of incrimination.

Testimony in the trial is scheduled to resume around 9:15 a.m., per the court’s daily schedule. The state could call on medical experts to testify on it’s central argument — that Floyd died after Chauvin knelt on his neck for 9 minutes and 29 seconds. Chauvin is charged with second-degree murder, third-degree murder and manslaughter.

RELATED: Watch Gavel-To-Gavel Coverage Of The Derek Chauvin Trial

WCCO-TV is live streaming the trial on CBSN Minnesota. Jason DeRusha is anchoring the coverage, and legal analysis is being provided by Joe Tamburino, a criminal defense attorney who is not affiliated with the case.

On Wednesday, the court heard from crime scene investigators who testified on the evidence they analyzed in the case. Much of the testimony surrounded the pills found in the back seat of the police SUV and the car that Floyd was driving. Floyd’s DNA was on the pills, which contained methamphetamine and trace amounts of fentanyl.

Bureau of Criminal Apprehension (BCA) investigators initially missed the pills in the back of the police SUV. The pills were recovered in January only after the defense asked for re-examination of the squad. “At the time I didn’t give it any forensic significance,” BCA forensic scientist McKenzie Anderson testified, concerning the pills. “The focus of it was processing the blood in the back seat.”

RELATED: Could His Mask Hamper Ex-Officer’s Image With Jurors?

Also on Wednesday, the attorneys questioned the initial lead BCA investigator in the case, James Reyerson. Nelson, Chauvin’s attorney, got Reyerson to agree that on body-worn camera footage Floyd can be heard telling officers that he “ate too many drugs.” It was a key point for the defense, which is trying to argue that Floyd died of underlining health conditions and a drug overdose, not Chauvin’s knee.

However, when prosecutors played a longer clip of the body-worn camera video for the court, Reyerson changed his answer on Floyd’s words. “I believe Mr. Floyd was saying, ‘I ain’t do no drugs,’” Reyerson said.