ABC News(DALLAS) — The former Dallas police officer accused of killing an unarmed man in his home took the stand in her own defense Friday, overcome with emotion as she told jurors about the moment she came face-to-face with the victim after opening the wrong apartment door.

“I was scared to death,” Amber Guyger testified, adding that her “heart rate just skyrocketed.”

Guyger walked into the apartment belonging to Botham Jean 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 was fired from the Dallas Police Department weeks after the shooting. She is charged with murder.

“I’m so sorry,” she said as she wept on the stand, her voice trembling. “I never wanted to take an innocent person’s life.”

“I wish he was the one with the gun that killed me,” she said, overcome with emotion.

Guyger testified Friday that on the night of the shooting she was tired from a long day at work and mistakenly parked on the wrong floor. 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 put the key into the lock that night, she said she noticed the door was “cracked open” and that putting the key into the lock forced the door open to the dark apartment. 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.

Guyger said she saw the silhouette of a figure, so she pulled her “gun out and I yelled at him.”

“Let me see your hands! Let me see your hands!” she said she shouted.

She told the jurors the figure was moving around and she could not see his hands, and that the man “was yelling, ‘Hey! Hey! Hey!’ in an aggressive voice.”

Guyger reenacted the next moment for the jurors, holding her right hand out as if she was holding a gun. Guyger said Jean was moving toward her when she fired.

Her attorney asked why she fired, and Guyger replied, “I was scared he was gonna kill me.”

After the shooting, Guyger said she realized she was not in her own apartment and “had no idea where I was at,” so she went outside to look at the apartment door.

The defense attorney played Guyger’s emotional call to 911 in which she repeatedly said she thought she was entering her apartment.

Guyger told the court she did a sternum rub on the victim, which is often performed by EMTs.

“I wanted him to keep breathing,” she testified. “The state he was in, I knew it wasn’t good.”

But during cross examination, prosecutors accused Guyger of not giving Jean undivided attention for CPR.

Guyger admitted to trying to perform a “little CPR,” but she said she kept getting up to figure out where she was and tell 911. Guyger also admitted to stopping CPR to text her married police partner and lover to come help.

Guyger also testified that she didn’t take her first aid kit out of her backpack to use and said she did not have any blood on her uniform or shoes.

During cross examination, Guyger said she could have called for help on her radio or backed out of the apartment instead of reaching for her gun. Speaking softly, she admitted her intention was to kill Jean when she pulled the trigger.

Dallas County Assistant District Attorney Jason Hermus told the jury in his opening statement that Guyger fired so quickly she gave Jean “no opportunity for de-escalation, no opportunity for him to surrender.”

“Bang, bang. Rapid,” Hermus said.

Later, Hermus continued grilling Guyger.

“So,” the prosecutor continued, “you could’ve taken a position of cover and concealment? You could’ve called for help on your radio, and you could have had the cavalry here in two minutes. Had you done one of those things, Mr. Jean probably would be alive today! Right?”

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,” Hermus said.

Defense attorney Robert Rogers denied that Guyger was planning a rendezvous that night with her partner, calling the prosecution’s assertion “speculation.”

Rogers in his opening argument 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.

Investigators later learned that 93 tenants had unintentionally parked on the wrong floor, Rogers said. He said another 46 tenants who lived on the two floors where Guyger and Jean resided had gone to the wrong apartment and placed their key in the door.

Marc Lipscomb, 31, an attorney at a Dallas law firm, lived on the third floor of that apartment complex and testified that he unknowingly walked into the wrong apartment one night, thinking it was his own.

“I just opened the door and I, as it turns out, was walking into the second floor apartment that was in the same spot [as mine on the third],” he testified Friday, adding that it wasn’t until he came face-to-face with a woman inside the apartment that he realized he was in the wrong one.

He also testified that he parked on the wrong floor of the apartment complex’s garage about 10 to 12 times. He said he would walk down the hall until he reached what he believed to be his door and then put in the key.

“Sometimes a red light would blink, at which point I’d realize I’m at the wrong apartment,” Lipscomb testified.

Jessica Martinez, 31, who lived on the third floor of the complex, testified Friday that she often had problems getting her key fob to work and that she had often found non-residents in the apartment’s pool area and stairwells.

She recounted one incident in which she said she was home “on my couch and I heard my key noise. And then the door opened and this man came inside.”

The man was holding a key, Martinez said. She said she yelled at hims to leave and “he walked outside and shuffled” to an apartment next door and used the key entered to enter that home.

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