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.KAREN READ TRIAL WITNESS FACES BRUTAL CROSS-EXAMINATION OVER VEHICLE DATAO'Keefe suffered "a classic blunt-trauma injury," Wolf said.O'Keefe fell backwards and hit his head, Wolf said, and the force of the impact fractured his skull and later resulted in "raccoon eyes," which look like black eyes."This is what happens when soft tissue hits a solid ground," he testified.Swelling in the victim's brain would have killed him under normal circumstances, usually within 24 to 48 hours, according to Wolf. Some victims have died in as little as one to three.In the January nor'easter, O'Keefe's body temperature also tanked. When paramedics found him at 6 a.m., his temperature was just 80 degrees, below the threshold for what medical professionals call "severe hypothermia."Wolf said he treated many patients with similar injuries early in his career, when he worked in a Minneapolis trauma center. The city can be brutally cold during winter. Many of the wounds were fatal. Some were inflicted on drunken patients who slipped on the ice. Others involved people who fell over after suffering a heart attack."This testimony from Dr. Wolf sets up the commonwealths argument for count 2, the involuntary manslaughter charge," said Grace Edwards, a Massachusetts defense attorney who is following the case. "The commonwealth will argue to the jury that if they cannot find that Karen Read caused John OKeefes death intentionally, counts 1 and 3, then her driving or sideswipe of him and then leaving him injured was the wanton and reckless act, which contributed to his death, then they should find Karen Read guilty of count 2."EXPERT WITNESS IN KAREN READ MURDER TRIAL CAUGHT WITH 'ERRORS' INFLATING HIS CREDENTIALSAccording to Wolf's bio at the Miami Neuroscience Center, he is a world-leading authority in his field and the clinic's director.A short cross-examination by defense attorney Robert Alessi discussed separate injuries that O'Keefe sustained, which were not connected to the head trauma that killed him.STATE TROOPER POINTS TO POSSIBLE WEAPON IN JOHN O'KEEFE DEATH AND IT'S NOT KAREN READ'S CAR"I thought Attorney Alessi did a good job redirecting Dr. Wolf from the back of the head to the front of the head and eliciting testimony that those injuries were likely not from a fall," Edwards told Fox News Digital. "This supports the defense theory that John OKeefe was not hit by a vehicle and suggests it was something else because of the laceration to his face and the injuries to the arm, and the investigation did not pursue any other leads to determine how John OKeefe sustained those injuries."Wolf started the day on the stand. After his testimony, Christina Hanley of the Massachusetts State Police Crime Lab returned to the witness stand. She is an expert on glass and plastic fragments who analyzed the broken cocktail glass found outside 34 Fairview Road and on the back bumper of Read's Lexus SUV, as well as pieces of the broken taillight.FOLLOW THE FOX TRUE CRIME TEAM ON XHer testimony had been interrupted at the early end of the day on Tuesday.She said Wednesday afternoon that some of the plastic debris recovered from O'Keefe's clothing was "consistent" with the materials used in Read's Lexus but could have come from another source with similar characteristics.During cross-examination, she revealed that none of the broken glass on Read's bumper matched the shattered cocktail glass found in the yard near O'Keefe.GET REAL-TIME UPDATES DIRECTLY ON THE TRUE CRIME HUBDefense 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.