A healthy person would have died under the conditions George Floyd faced during his attempted arrest in May 2020, said Dr. Martin Tobin, a lung and critical care specialist at Edwards Hines Jr. VA Hospital and Loyola University’s medical school in Chicago.

The defense for former officer Derek Chauvin plans to argue heart problems and the fentanyl and methamphetamine in Floyd’s system killed him, not Chauvin kneeling on his neck.

Tobin, a witness for the prosecution, on Thursday rejected that explanation, saying Chauvin did not remove his knee until more than three minutes after Floyd’s body had run out of oxygen.

Tobin told jurors someone can speak until the airway narrows to 15 percent, but that does not mean the person will be breathing even a few seconds later. He said Floyd appeared to have sufficient oxygen for the first five minutes under Chauvin’s knee but experienced brain damage and went unconscious soon after.

This story originally appeared in WORLD. © 2021, reprinted with permission. All rights reserved.