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DALLAS, Texas — Amber Guyger, the ex-Dallas police officer charged with killing a 26-year-old man in his own apartment while she was off duty, wept in court Friday morning as she testified in her own defense.

Guyger, who’s charged with murder in the death of Botham Jean, had been asked by one of her lawyers to describe the way she approached the door to what she thought last September was her apartment.

In a light blue dress and a dark cardigan, Guyger’s lips began to quiver as she broke down in tears while stepping down from the witness stand to demonstrate how she carried her police equipment in one hand and tried to open the door with the other.

The judge immediately called a recess, and the jury left the courtroom. If convicted, Guyger faces up to life in prison.

Guyger had earlier testified about her childhood growing up in Arlington, her affair with her married police partner and her training as a police officer. She also recounted wanting to become an officer at age 6.

“I wanted to help people, and that was the one career that I could help people,” she said.

The prosecution, which rested on Thursday, was expected to grill Guyger, possibly also questioning her about her actions after she shot Jean.

Jean was on the couch in his shorts, watching TV and eating vanilla ice cream, when Guyger walked in and fired, Jason Hermus, a Dallas County prosecutor, told jurors this week.

Guyger has told police she mistakenly walked into the wrong apartment and thought she saw a burglar. Guyger lived in Apartment 1378, one floor below Jean’s unit.

Dallas Police fired Guyger shortly after the shooting.

Guyger should have known she was in the wrong unit, prosecutors say

Guyger missed several signs indicating she was on the wrong floor and at the wrong apartment, prosecutors argued.

Several witnesses were questioned on the differences between Guyger’s and Jean’s apartments in an effort to demonstrate the former officer should have realized she was in the wrong unit before she opened fire.

For example, Dallas police Det. Stephen Cleary pointed out that Guyger’s apartment had a wooden board displaying photos hanging on the wall, a bookshelf in the corner and a small half-circle table with a vase of flowers against the wall.

The wall behind Guyger’s couch was bare, the photos showed.

But Jean’s apartment had art on the wall behind the couch, an ottoman and rug in the living room, and a workstation near the bar, Cleary testified.

The defense countered by pressing witnesses on the similarities in the hallways leading to their apartments.

This week, Texas Ranger David Armstrong testified that of the nearly 300 residents that investigators interviewed at the complex, nearly a quarter of those who lived in the third and fourth floors had previously put their keys in the wrong door. Even more had parked on the wrong floor and walked to the wrong apartment.

She should have focused on saving Jean but texted her partner, prosecutors say

Prosecutors also tried to show Guyger did not follow department burglar protocol for a burglary call. Guyger should have taken cover and called for backup, per protocol, at least one of her fellow officers testified.

But the defense argued since Guyger was off-duty and thought she was walking into her own home, she should not be held to that standard.

She was fatigued after working 40 hours in four days and was on “autopilot” when she parked on the wrong floor in the garage where the floors are not clearly marked, defense attorney Robert Rogers said in opening statements on Monday.

As Guyger entered the apartment, she looked up and believed she saw an intruder about 30 feet from her in the dark, Rogers said.

The locking mechanism on Jean’s door was damaged, Armstrong testified, affecting the door’s ability to shut properly at times. Guyger’s defense team said that was one of the reasons she thought someone was burglarizing her home.

But after the shooting, Guyger was derelict in her efforts to save Jean after shooting him, prosecutors said, pointing to a 911 call she made shortly before 10 p.m. in which she said 19 times she was in the wrong apartment.

“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 said.

Guyger said she performed first aid on Jean, an affidavit said.

Guyger sent two text messages to her partner on the force, whom prosecutors said she was intimate with — one at 10:02 p.m. saying, “I need you … hurry,” and another a minute later saying, “I f***ed up,” according to the testimony.

Authorities recovered those text messages, but Guyger allegedly deleted other messages, Hermus said. Guyger should have devoted all of her attention to providing first aid to Jean, Hermus said, instead of texting her partner.

Dallas Police officer Tu Minh Nguyen testified Thursday Jean was “still alive” when officers started doing CPR, but his condition was “very faint” and he could be heard making grunting noises, the officer said.