John O’Keefe died from falling backwards and hitting his head on frozen ground, according to a Yale-educated brain surgeon who testified Wednesday in the murder trial of Karen Read.

Read, 45, is accused of killing her then-boyfriend, the 46-year-old O’Keefe, by hitting him with her 2021 Lexus SUV on Jan. 29, 2022, then leaving him to die on the ground in a blizzard in Canton, Massachusetts, about 20 miles south of Boston.

The head trauma and skull fractures he sustained, coupled with hypothermia from the cold, would not have killed him immediately, according to Dr. Aizik Wolf, who testified he treated many similar injuries in his career working in Minneapolis.

“The only way he could get this kind of an injury was to fall backwards, hit the back of his head, and then the resulting energy forces going into his brain, into the base of his skull,” he told the jury during questioning from special prosecutor Hank Brennan. 

Defense attorney Alan Jackson had her explain that the only thing any of the bumper glass matched was a glass sample recovered by former Trooper Michael Proctor, who was fired in March after an internal probe into inappropriate text messages he sent during the investigation.

Earlier in the trial, the defense played video showing Proctor standing near the rear of the vehicle, out of camera view, while it was at the Canton Police Department headquarters.

Proctor, through his family, has maintained that his investigation was in line with the evidence and conducted with integrity.

Read could face life in prison if convicted of the top charge, second-degree murder. She is also accused of drunken driving, manslaughter and leaving the scene of a deadly accident.

Fox News’ Andrew Fone contributed to this report.