imaginima/iStock(DALLAS) — The former Dallas police officer accused of killing an unarmed man in his apartment took the stand in her own defense on Friday, overcome with emotion as she was instructed to tell the jurors what happened when she opened the apartment door.“I was scared to death,” Amber Guyger testified, and said her “heart rate just skyrocketed.”Guyger, who is white, walked into the apartment belonging to Botham Jean, who is black, on Sept. 6, 2018, allegedly believing it was hers. Guyger was still wearing her police uniform when she fired two shots at Jean, who was eating ice cream in his unlocked apartment.Guyger, who was fired from the Dallas Police Department weeks after the shooting, is charged with murder.Guyger, speaking calmly and quietly, testified Friday that she mistakenly parked on the wrong floor that night; she said the parking floors at her apartment building were not clearly marked.She re-enacted how she reached the apartment door, with her backpack, lunchbox and police vest in her left hand, and testified that she heard the sound of someone walking inside.When Guyger, then 30, put the key into the lock that night, she noticed the door was “cracked open” and that putting the key into the lock forced the door open to the dark apartment, she testified. Guyger said earlier she had experienced problems getting the door to lock completely at her apartment.Jean, an accountant for the international auditing firm PricewaterhouseCoopers, was sitting on his couch when Guyger opened the door, prosecutors said.Before Jean could take a few steps toward the door, Guyger leveled her gun and fired twice, Dallas County Assistant District Attorney Jason Hermus said.“No opportunity for de-escalation, no opportunity for him to surrender. Bang, bang. Rapid,” Hermus told the jury in his opening statement.Hermus said Guyger’s apartment was directly beneath Jean’s fourth-floor unit. Not only did Guyger mistakenly park on the wrong floor of the complex, she walked down a long hallway, passing 16 different apartments, but failed to realize she was not headed to her front door, Hermus said.Hermus said Guyger appeared to be planning a rendezvous with her police partner and lover. Hermus showed the jury text messages Guyger sent her partner moments before the shooting and argued that during that communication, Guyger became distracted and confused about where she was.“In the last 10 minutes of Bo’s life, Amber Guyger made a series of unreasonable errors, and unreasonable decisions, and unreasonable choices — the kind of choices and decisions that only she could have stopped,” Hermus said.Defense attorney Robert Rogers said in his opening argument that Guyger was exhausted from working 40 hours in four days, including a long overtime shift helping a SWAT team arrest three robbers.He described the configuration of the apartment complex, where Guyger had lived for about two months, as “a confusing place” with floors in the parking garage and apartment doors not clearly marked.He painted the picture of Guyger entering the apartment and seeing the figure of a large individual inside coming toward her, yelling, “Hey! Hey!’ and drowning out her orders for him to show her his hands.“After this incident, the investigators interviewed and learned that 93 tenants had unintentionally parked on the wrong floor,” Rogers said.He said another 46 tenants who lived on the floors where Guyger and Jean resided had gone to the wrong apartment and placed their key in the door.Rogers denied that Guyger was planning a rendezvous that night with her partner, calling the prosecution’s assertion “speculation.”This is a developing story. Check back for more updates.Copyright © 2019, ABC Radio. All rights reserved.