Testimony concludes in Chauvin trial with rebuttal witness

Testimony wrapped Thursday in the trial of former Minneapolis Police Department officer Derek Chauvin, who is charged in the death of George Floyd.

Chauvin, who kneeled on Floyd’s neck for more than nine minutes during a May 25 arrest, is charged with third- and second-degree murder and second-degree manslaughter. Closing arguments are expected Monday.

On Thursday, the defense rested its case. The prosecution then brought back one of their expert witnesses, pulmonologist Dr. Martin Tobin, to offer a rebuttal to testimony offered by a defense witness Wednesday.

On Wednesday, Dr. David Fowler, former Maryland chief medical examiner, testified that he believed the cause of Floyd’s death was “undetermined.” He cited the possible effects of Floyd’s heart conditions, stress levels and drug use, all of which have been at the center of the defense’s case.

The prosecution and expert witnesses called by the prosecution have argued that Floyd died due to a lack of oxygen, or asphyxia, caused by Chauvin's restraint.

Fowler also suggested that carbon monoxide poisoning could have played a part, pointing to an exhaust pipe of a nearby squad car while Floyd was in the restraint. But Fowler acknowledged that without testing Floyd’s blood composition, there was no way to confirm or rule out the possibility.

But following Fowler’s testimony, Hennepin County Medical Examiner Dr. Andrew Baker disclosed that Floyd’s carbon monoxide levels were tested and available.

Judge Peter Cahill said Thursday that there would be a mistrial if Tobin spoke about the test results, which were not previously admitted as evidence. Cahill said Tobin could speak on environmental factors at the scene of the arrest and the likelihood they could cause carbon monoxide poisoning.

“If he even hints that there are test results that the jury has not heard about, it’s going to be a mistrial, plain and simple,” Cahill said.

Tobin was able to testify on the oxygen saturation in Floyd’s blood. According to autopsy results, Floyd’s blood contained 98% oxygen saturation, meaning the maximum saturation of carbon monoxide would be 2%. Tobin said normal levels of carbon monoxide are around 0% and 3%.

Fowler had previously asserted Floyd’s carbon monoxide levels could have been between 10% and 18%.

“The maximum of carbon monoxide would be 2%... It doesn't even tell you that it’s 2%, it could be something else,” Tobin said.

Following Tobin’s testimony, the prosecution also rested its case.

Earlier on Thursday, Chauvin told Cahill he would invoke his 5th Amendment right not to testify before the jury, which would have subjected him to cross-examination by the prosecution.