CNN — After many months of courtroom showdowns, conspiracy theories and accusations of a cover-up, the trial in the killing of Boston Police Officer John O’Keefe starts today.

O’Keefe’s body was found in the snow on January 29, 2022, outside the home of a fellow Boston police officer in Canton, Massachusetts. His girlfriend, former finance professor Karen Read, has pleaded not guilty to second-degree murder, vehicular manslaughter while intoxicated and leaving the scene of a collision.

Residents of Canton and neighboring suburbs have spent months debating two potential scenarios: Was O’Keefe beaten inside the officer’s house and tossed outside to die in the snow? Or did his girlfriend fatally strike him with her black Lexus SUV?

Protesters have accused local authorities of a cover-up to protect the homeowner and have stormed city council meetings to demand answers. Some have formed private Facebook pages and frequented blogs to discuss intricacies of that fateful night, turning what began as a local homicide case into a national sensation.

Jury selection starts this week in Norfolk County, south of Boston. The case’s heavy publicity complicates the process of picking an impartial jury, which may come down to selecting jurors who are familiar with O’Keefe’s killing or have read about it but have not formed an opinion, said Daniel Medwed, a criminal law professor at Northeastern University.

“It’s fair to say a large number of people in Massachusetts know about this case,” Medwed told CNN. “What happens in these jury selection processes is that the lawyers will say, ‘Well, given what you know, can you still be fair’? It’s possible that there could be 12 citizens, residents of this county, who haven’t made up their mind.”

The case has sharply divided the Boston suburb of 24,000 people. As the trial gets underway at the Norfolk County Superior Court building in Dedham, Massachusetts, here are the key highlights.

The case comes down to a crucial six-hour window

The case revolves around the six hours before O’Keefe’s body was discovered that winter night. Surveillance footage captured video of him and Read on a night out on January 28, 2022 drinking at two Canton bars and meeting up with friends, including the fellow officer.

Shortly after midnight, the couple climbed into Read’s SUV and drove to the officer’s home on Fairview Road in Canton for an after-party, court documents show.

Read, 44, has said she dropped off O’Keefe at the Fairview Road house, then drove to his home to rest because she wasn’t feeling well, according to court documents. She said she later woke up in the predawn hours and panicked when she realized he was not home.

She told investigators she then called two female acquaintances and the three women drove through the streets of Canton in near white-out conditions, looking for O’Keefe and calling his name, court documents show.

Read spotted her boyfriend’s body in the front yard of the house, covered in snow, and rushed to perform CPR on him, court documents show.

Read and her legal team, including attorneys Alan Jackson and David Yannetti, have argued their client is being framed. Jackson told CNN that he believes O’Keefe entered the Fairview Road house that night and got into an altercation with someone inside.

“I think that confrontation got physical, and he was beaten to a point of unconsciousness,” Jackson said. “This was a coverup … he was murdered inside that house and his body placed outside.”

But the prosecution alleges that the couple got into an argument that led to O’Keefe getting out of the Lexus, after which a drunken Read struck him with her vehicle and fled, leaving him to die in the snowy cold.

In case documents and in court, Read’s attorneys have said they believe one of the two female acquaintances, the homeowner’s sister-in-law, is part of a cover-up to protect the people inside the house and frame Read for the crime.

A forensic search of the woman’s phone revealed a Google search for the phrase, “Ho(w) long to die in cold” hours before O’Keefe was found, according to court documents.

But the woman has not been charged with a crime and her attorney, Kevin Reddington, has told local media that allegations of her involvement in a cover-up are baseless.

Meanwhile, Norfolk County District Attorney Michael Morrissey has said allegations that a network of law enforcement agencies conspired to frame Read are not plausible.

“These people were not part of a conspiracy and certainly did not commit murder or any crime that night,” Morrissey said. “The idea that multiple police departments, EMTs, fire personnel, the medical examiner and prosecuting agencies are joining in … a vast conspiracy should be seen for what it is — completely contrary to the evidence and a desperate attempt to reassign guilt.”

The furor over the case has divided the town

The case has been marked by legal wrangling for months. Last week, both the defense and prosecution filed a flurry of motions over evidence they want to introduce or exclude from the trial. For example, prosecutors are seeking to show jurors details from a December 2021 trip the couple took to Aruba, arguing that it shows strains in the couple’s relationship.

The US Attorney’s Office for the District of Massachusetts has launched a federal probe into Read’s arrest and prosecution. In February, federal officials released some 3,000 pages of documents about their investigation. Most of the information was withheld from the public.

And last month, the Massachusetts State Police announced an investigation into a state trooper who is involved in the case. The agency did not elaborate on whether the alleged violation is related to the charges against Read.

The investigation was announced the same week Read’s defense team alleged the trooper did not fully disclose his relationship with key witnesses in the case. Norfolk County Assistant District Attorney Adam Lally accused the defense of using the relationships to distract from Read’s alleged guilt, CNN affiliate WFXT reported.

“It’s a three-card Monte trick. You know, card trick. On the corner, on the side. Look at all of this. Look at this relationship. Look at that relationship,” Lally said.

In November, Canton residents voted for an independent investigation into the police department after a special town meeting that focused on Read’s case. At the time, Canton Police Chief Helena Rafferty told CNN that investigators found “absolutely no evidence of a cover-up in the tragic death of John O’Keefe.”

Meanwhile, pretrial hearings have drawn protesters wearing “Free Karen Read” sweatshirts and carrying placards with similar messages. In response Norfolk County Superior Court Judge Beverly Cannone issued an order establishing a “buffer zone”around the courthouse to keep protesters away and restrict what they are wearing.

“No individual may demonstrate in any manner, including carrying signs or placards, within 200 feet of the courthouse complex during trial of this case. …. No individuals will be permitted to wear or exhibit any buttons, photographs, clothing, or insignia relating to … any trial participant,” the order said.

In ordering the buffer zone, Cannone said there have been documented cases of protesters shouting at witnesses and confronting family members outside court.

“There is a substantial risk that the defendant’s right to a fair trial will be jeopardized if prospective jurors are exposed to the protests and messages displayed on signs,” Cannone wrote.

Read’s supporters have argued the order violates their First Amendment rights.