She shot and killed the PriceWaterhouseCoopers accountant, she said, because she feared Jean was going to kill her after she entered his apartment on September 6, 2018, believing that it was her own.
She says she mistook his fourth-floor unit for her own, which was right below Jean's, and thought he was a burglar when she stepped inside the dark room.
When prosecutors asked why she didn't back away and radio for help once she suspected a break-in, Guyger said that entering the apartment "was the only option that went through my head".
Amber Guyger broke down while recalling approaching her neighbor Botham Jean's door, leading the judge to call for a brief break so she could compose herself. The prosecution, which rested on Thursday, is expected to grill Guyger, possibly questioning her about her actions after she shot Jean.
At one point when the jury had been sent out of the courtroom, Texas Ranger David Armstrong - who led the investigation into the shooting - said he did not believe Guyger had committed a crime when she shot Jean.
Hermus sharply questioned Guyger why she performed virtually no CPR on Jean, and why in her panicked call to 911 just after the shooting she not once said she thought Jean had a weapon or that she had been scared for her life.
A former Dallas police officer says she was "scared to death" when she opened what she thought was her apartment door a year ago and saw a silhouetted figure standing in the darkness inside.
Speaking about the day of the shooting, Guyger testified that she was exhausted on September 6, 2018, after a almost 14-hour day and "just ready to go home" when she left work.
Friday's testimony marked the first time the public has heard directly from Guyger about the events that led to Jean's death. She testified that when she put the key into the lock she noticed the door was ajar. She says she drew her service weapon because she thought someone was in her home, and then she told the silhouetted figure inside: "Let me see your hands!"
"Let me see your hands!"
"I didn't say (he was coming toward me) but I know he did", Guyger said. Rivera, she said, typically called her, but she never called him because "I knew it was wrong and I never knew where he was".
The former Dallas police officer who fatally shot her unarmed black neighbor in his apartment began crying and shaking on the witness stand as she started describing entering his home that night.
Just before the end of her direct examination by defense attorney Toby Shook, Guyger apologized for killing Jean.
It never entered her mind, she would tell prosecutor Jason Hermus on cross-examination, to follow another part of her DPD training - to retreat and wait for backup in order to maintain her safety.
Gugyer, who was off duty but in uniform at the time, was later fired.
The shooting attracted widespread attention because of the unusual circumstances and also because it was one in a string of shootings of unarmed black men by white police officers. Guyger should have taken cover and called for backup, per protocol, at least one of her fellow officers testified. They say she fired in self-defense after confusing his apartment with her own and mistaking the 26-year-old accountant from the Caribbean nation of St. Lucia for a burglar.