Monday, one of Dallas' biggest trials of the 21st century is set to begin at the Dallas County Courthouse on Riverfront Boulevard. Amber Guyger, a former Dallas Police Department officer, is charged with murdering Botham Jean, a 26-year-old PriceWaterhouseCoopers employee.

Guyger shot Jean, who lived in the apartment immediately above her own at the South Side Flats complex near DPD headquarters in The Cedars, after getting off work on Sept. 6, 2018. Guyger believed, she would later tell police, that Jean was an intruder in her own apartment, not realizing that she was on the wrong floor until after she'd shot him.

Here's a guide that, hopefully, will help you navigate the trial, its media coverage and its aftermath.

Why is Guyger charged with murder, and not a lesser crime like manslaughter or criminally negligent homicide? Guyger is charged with murder because she shot Jean on purpose. In Texas, someone commits manslaughter when they "recklessly cause the death of another individual." If Guyger had shot through the door and inadvertently hit Jean, for instance, she might be on trial for manslaughter, according to legal experts.

How much prison time does she face, if convicted? If Guyger is convicted, she faces 5-99 years in prison. She and her legal team have asked that her sentence be decided by her jury, if necessary.

What do we know about Guyger? Not much. She'd been a DPD officer for four years at the time of the shooting. In 2017, Guyger shot a drug offender who took her Taser. Any social media presence she might have had before the shooting — except for her Pinterest account — was long gone by the time she was publicly identified. In the days, weeks and months that have followed Jean's death, Guyger and her family have remained quiet.

Botham Jean speaks at his alma mater, Harding University. courtesy Harding University

What do we know about Jean? Jean, a native of Saint Lucia, attended Harding University in Searcy, Arkansas. During his time at the school, he frequently led Harding's daily chapel services and served as a resident assistant. Levi Heasley, a friend of Jean's from Harding, talked to the Observer last year about how their relationship began.

"They'd have to come and check whether or not you were in your room every single night. Most RAs were like, 'OK, cool, you're there,' but he would come in and say, 'Hey, what's going on? How was your day?'" Heasley said. "He genuinely cared and would talk to every single person on the hallway to make sure their day was all right and see if they needed anything — just to talk, or just anything. We started to hang out more and just talk and laugh and hang out outside of class because he was just fun to be around."

After graduating from Harding, Jean took a job with PriceWaterhouseCoopers and moved to Dallas. Once in Texas, he attended Dallas West Church of Christ. In the year that's separated Jean's death from Guyger's trial, Jean's family has made frequent trips to Dallas calling for what they believe will be justice for their son.

“I am indeed satisfied with the indictment for murder of Amber Guyger because I truly believe that she inflicted tremendous evil on my son,” Jean's mother, Allison Jean, said after Guyger was indicted for murder. “I look forward to the next step, which is a conviction of murder for Amber Guyger and more so to the penalty, which will cause her to reflect on the pain she has caused.”

What's Guyger's defense? It's unlikely that Guyger's defense team will quibble over the basic facts of the case. Guyger, in both interviews with police and a 911 call made in the immediate aftermath of the shooting, has admitted to shooting and killing Jean.

Instead, the case will hinge on a legal concept, enshrined in the laws of Texas and several other states, known as "mistake of fact."

Here are the basics, with some help from Dallas criminal defense attorney Pete Schulte and Cornell Law School professor Stephen Garvey.

"She clearly, based on what we do know, has the defense of what we call mistake-of-fact," Schulte said late last year. "If she can show to a jury that her mistake-of-fact led to this and the jury finds that it was reasonable, then she's entitled to an acquittal, because our criminal laws don't want to criminalize accidents. That's for the civil courts."

If a jury believes that Guyger reasonably thought she was entering her own apartment and that Jean had broken into her apartment when she shot him, she's covered by Texas' self-defense statute, which presumes that a person is "justified in using force against another" if he or she had "reason to believe that the person against whom the force was used ... unlawfully and with force entered, or was attempting to enter unlawfully and with force, the actor's occupied habitation, vehicle, or place of business or employment."

"It's standard mistake of fact," Garvey told the Observer this week. "She makes a mistake of fact about where she is and then that mistake feeds into the statutorily relevant facts about whether or not she reasonably believed that (Jean) was there unlawfully and entered with force."

What about the prosecution? Barring the introduction of some surprise evidence, prosecutors will argue that the mistakes Guyger made were unreasonable. Jean had a red doormat at his door, Guyger did not. Guyger told police that Jean's door was ajar, but her key would not have opened his door lock if that weren't the case — and investigators obtained a warrant for data from the company that made South Side Flats' electronic door locks.

How long is the trial expected to last? There's no set timetable, but Dallas County District Judge Tammy Kemp suggested during jury selection that jurors should expect to be sequestered for as long as two weeks.

What kind of experts can we expect to hear from? The defense's list of potential expert witnesses includes Charles Czeisler, a Harvard-based researcher with expertise in circadian and sleep disorders. Guyger was reportedly on the tail end of a 15-hour shift when she shot Jean, and the Dallas Police Association has cited fatigue as a potential reason for the shooting to the media.

In addition to Czeisler, Guyger's defense also lists Marc Green as a potential witness. Green, from Toronto, has made frequent appearances in U.S. courts, according to his CV, to testify about issues of human perception, like eyewitness identification, visibility and reaction times. Michael Haag, a shooting scene reconstruction specialist from New Mexico, is also on the defense's list.