A forensics expert zeroed in on two pieces of evidence ahead of Karen Read’s murder trial — the autopsy and the way the victim’s clothes were handled — and said he believes the medical examiner’s testimony will be pivotal.

Read allegedly hit her boyfriend, Boston Police Officer John O’Keefe, with her car and left him to die in the snow, prosecutors said. Read denied the allegations and claimed there was a cover-up to frame her.

O’Keefe’s official cause of death is listed as “undetermined,” which sets up the medical examiner as the “big star” of the trial, forensics expert John Scott Morgan told Fox News Digital. 

“I urge everybody that’s following this case to really pay close attention to what the medical examiner says, because they will be asked to explain the logic behind listing this as an undetermined,” Morgan said. “I would expect the defense to particularly focus in on that question, and it will be framed in a manner in which they will say, ‘Well, you know, we’ve got the prosecutor here that is saying that this is, in fact, a murder. What is it, doctor, what is keeping you from ruling this as a homicide?”

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The case goes back to 2022 in the Boston suburb of Canton, Massachusetts, where O’Keefe was found dead. Both O’Keefe and Read were drunk that night, according to court documents.

The trial started with jury selection last week after nearly two years of divisive rhetoric on both sides and an undercurrent of controversy fueled by a federal probe into the defense’s cover-up allegations.

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On Wednesday, a full jury was selected among hundreds of prospective jurists, setting the stage for what’s expected to be a lengthy and tense trial. Read’s supporters and adversaries have been clashing outside the courthouse. 

On Thursday, several pretrial motions are expected to be resolved, and opening statements are scheduled to start Monday.

O’Keefe suffered multiple wounds, including skull fractures consistent with blunt-force trauma that led to bleeding in the brain, swollen black eyes and several lacerations and abrasions to his right arm and hands.

The prosecution alleges the injuries were sustained when Read hit him with her car, while the defense says the injuries were suffered during a fight inside the house and a dog attack. 

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“That’s very specific information,” said Morgan, who spent over 20 years in the New Orleans coroner’s office and with the Fulton County Medical Examiner in Atlanta before becoming a professor at Jacksonville State University in Jacksonville, Alabama.

The key is when this information about a possible dog bite was relayed to the medical examiner. 

If the medical examiner didn’t know about the dog bite defense during the autopsy, the examiner likely wouldn’t have attempted to get evidence, like dog hair or a saliva swab, to test if there was canine DNA, Morgan said. 

WATCH: Morgan previews potential arguments for O’Keefe’s injuries

‘There’s one issue here that has been particularly troubling to me’

Morgan said how O’Keefe’s clothing was removed during life-saving efforts, how they were preserved and the chain of custody “is very important here.”

If reports about clothing being piled up in the corner of a trauma room are accurate, potential evidence is compromised, he said.

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“Are we talking about hours? Days? Weeks? Because the longer you wait to submit this, the less secure it is,” Morgan said, “And if you can’t account for it 24/7, you spoil the chain of custody. And, at that point, there’s little or no accountability. You don’t know who’s come in contact with these items.

“It can be very delicate. And once you have that evidence as a forensic investigator, you need to know how it was packaged and who packaged it.”

He used the example of the O.J. Simpson murder case, which included over 100 exhibits of DNA evidence that his lawyers essentially discredited by arguing investigators botched the removal, collection, handling and processing of evidence, including bloody clothes. 

“Reflect back to the O.J. Simpson case, where one of the detectives had been mentioned of riding around with blood samples in their car before they were ever submitted into evidence,” Morgan said. “All kinds of things can happen, particularly with blood evidence like that, because it is fragile.”

Read’s arrest and how a blogger fueled the fire

Read was arrested Feb. 2, 2022, and charged with second-degree murder, manslaughter while operating under the influence of alcohol and leaving the scene of an accident, causing injury and death. She pleaded not guilty to all charges.

“I did not kill John O’Keefe. I have never harmed a hair on John O’Keefe’s head,” Read told ABC News in August.

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The case split the otherwise quiet suburban town, and a local blogger, Aiden Kearney, who goes by the nickname “Turtleboy,” riled up the “Free Karen” side of the debate. 

He is often seen with a cellphone camera and bullhorn leading demonstrations and trumpeting Read’s law enforcement cover-up defense.

The Norfolk County District Attorney’s Office alleged he crossed a line by intimidating witnesses, and he was arrested in October, enraging his loyal followers. 

The prosecutor alleged Kearney “showed up” at sporting events of witnesses’ children and “made scenes,” harassed and photographed witnesses at their homes and jobs and instructed followers of his blog to do the same.

GET REAL-TIME UPDATES DIRECTLY ON THE TRUE CRIME HUB 

Kearney’s lawyer told the judge his client “vehemently denies” the accusations when Kearney pleaded not guilty, saying his client’s opinions are protected by the First Amendment.

Kearney was indicted on over a dozen felonies involving witness intimidation. He also served 60 days in jail for violating a protective order, but he has since been freed and is waiting for his own trial.

“The influence of media, social media, the sidebars with the turtle blogger. All the information that’s been going back and forth from the DA’s office and the defense team. I think it’s going to be a long road to pick an impartial jury,” Suffolk University Law Professor Christopher Dearborn told CBS News.

Fox News Digital’s Mitch Picasso contributed to this report.