(CNN) Amber Guyger, the former Dallas police officer charged with killing Botham Jean in his own apartment, missed numerous signs indicating she was not on the right floor or at the right apartment the night of the shooting, a prosecutor said Monday.

The fourth floor of the garage where she parked after her 13.5-hour shift was open air, unlike her parking area on the third floor, Jason Hermus, a prosecutor with the district attorney's office, told jurors.

She failed to notice a skylight, a neighbor's decorative planter, Jean's red doormat and differences in the hallways, Hermus said.

Once she opened the door to Jean's apartment, he continued, she didn't notice other differences, including a missing table, clutter on the counter and the aroma of marijuana, the prosecutor said. Jean had smoked marijuana to help treat his ADHD after he stopped taking his prescribed medication, which had an adverse effect on him, his sister told jurors.

Onlookers were turned away from the courtroom after it reached capacity.

But Guyger's attorney said she was fatigued from working, and was on "autopilot" when she parked her car and walked down the complex's nondescript hallway and encountered what she thought was a burglar in her apartment. The shooting was "nothing short of an epic tragedy," Robert Rogers told jurors.

The former officer killed Jean in his apartment on September 6, 2018, believing it was her unit, which was one floor below, police said. She was indicted on the murder charge more than two months later. She has pleaded not guilty, and faces up to life in prison if convicted.

The shooting sparked days of protests in Dallas and calls for the white officer to be charged for killing the 26 year-old unarmed black man. Civil rights lawyer Benjamin Crump, one of the Jean family attorneys, said the shooting was another example of the threat of violence black people live with.

Guyger's trial opened with District Judge Tammy Kemp expressing disappointment in Dallas County District Attorney John Creuzot for doing a television interview that aired Sunday night, despite a gag order in the case.

In the interview, Creuzot spoke about how observers were "misinterpreting" the facts of the case and how murder was the appropriate charge for Guyger.

Kemp said she intends to sequester the jury for the proceedings.

'In autopilot'

Guyger had worked 40 hours in four days during the week of the shooting, Rogers said. She was so tired that she asked her supervisor to take a day the next day.

She was not paying attention when she parked in the garage, where the numbers are not clearly marked on the floors, Rogers said.

"Was that evil of her to do? Was that evil of her not to count the floors? Was that just a reasonable reaction to 'oh my gosh I found a good spot,'" Rogers said.

JUST WATCHED CNN granted access to Botham Jean's apartment Replay More Videos ... MUST WATCH CNN granted access to Botham Jean's apartment 03:30

Rogers said the hallways, apartment doors and lights all looked the same as she approached Jean's door.

"Amber Guyger was in autopilot. She got to the door and she put her key fob and in one motion, the door is opening, and it doesn't make sense because normally you have to turn the handle," Rogers said.

Guyger looked up and saw the man she thought was the intruder about 30 feet from her, her attorney said.

"I'm sure, he's alarmed. But she's thinking, 'Oh my God. There's an intruder in my apartment.' And she's face-to-face with him; she's within 10 yards of him. And he starts approaching her," Rogers said.

She drew her gun, expecting the sight of the weapon would make him stop and ordered him to show his hands, Rogers said.

"But he drowns her out and he's yelling, 'hey, hey.' And he's 25 feet and then he's 20 feet, and it's happening like this," Rogers said, snapping his fingers.

Rogers said his client "firmly and reasonably believed that she had no choice. She had no options but to use her gun to keep from dying."

Guyger texted partner on the force after shooting

The accountant was at home in his shorts, watching TV and eating vanilla ice cream when Guyger walked through the front door and fired twice, Hermus said.

"He was doing no harm to anybody, which was his way," the prosecutor said.

Hermus said that under the circumstances, protocol demanded that she take cover and call for backup instead of opening fire. One bullet missed, but the other bullet hit Jean in the chest and traveled downward through his heart, lung, stomach and intestine before resting between his stomach and back, he said.

The trajectory suggests Jean was either getting up from a chair when Guyger fired, or he was on his knees, trying to hide from her, Hermus said.

Following the shooting, he said, Guyger made a 911 call in which she repeatedly said she thought she was in her own apartment and never indicated that Jean posed any threat, but the call also demonstrates that her foremost concern was not helping the man she'd just shot.

JUST WATCHED December 2018: Police officer indicted in Botham Jean's death Replay More Videos ... MUST WATCH December 2018: Police officer indicted in Botham Jean's death 02:56

"When you listen critically to what she is saying, you are going to hear that she is as concerned or more concerned about how this is going to affect her than this poor guy on the floor next to her," Hermus told jurors.

While she was on the phone with a 911 dispatcher, she also sent texts to her partner on the force, with whom she was intimate, saying, "I need you hurry" and "I f***ed up," Hermus said. He explained that while investigators were able to recover those texts, they were unable to obtain others because Guyger allegedly deleted them in the day or two after the shooting.

Rather than texting a lover, Hermus said, Guyger should have devoted 100% of her attention to providing first aid -- or at the very least, comfort -- to Jean as he lay wounded on the floor.

JUST WATCHED Botham Jean's minister: Sadness can't be erased Replay More Videos ... MUST WATCH Botham Jean's minister: Sadness can't be erased 01:29

According to a copy of the 911 call, Guyger told a dispatcher 19 times: "I thought it was my apartment."

He said Guyger knew she needed help from EMS.

"She knows that she's messed up. She knows she's made a tragic mistake. But it's not out of evil. It's not out of careless recklessness," Rogers said.

Rogers said Guyger also reached out to her partner on the force because they had been in many difficult situations together. The two had been involved before but not at the time of the shooting, Rogers said.

Guyger exchanged sexually explicit messages on day of the shooting with her partner, Martin Rivera, including one message in which Rivera asked when he could come over, Rivera testified. They also exchanged pictures but Rivera said he said he didn't recall the photos he sent to her.

The two talked for more than 16 minutes on the night of the shooting, Rivera acknowledged.

That call ended shortly before 10 p.m., Hermus said. Minutes later, Guyger texted Rivera telling him to hurry and used the expletive, Hemus said.

Rivera said he deleted the text message exchange with Guyger from the day of the shooting.

"That's not something that I would want to be reminded of, speaking of the night. And I don't keep messages saved unless it's of an importance to me," he said.

During cross-examination from Rogers, Rivera testified he had never been to Guyger's apartment, and had no intention of going there that night.

The two were not having a regular sexual relationship in September 2018, he said.

The messages, Rivera said, were "flirting, teasing, mainly."

"What you will see and hear and experience is the perfect storm of innocent circumstances that all came together," Rogers said.

Jean died at a hospital that night.

Guyger was arrested for manslaughter three days after the shooting. The Dallas Police Department, which hired her in November 2013, fired her on September 22, 2018.

Guyger is expected to take the stand when the defense presents its case.