Speaking publicly for the first time about the night he shot 911 caller Justine Ruszczyk, ex-Minneapolis police officer Mohamed Noor told jurors at his trial of hearing a bang and reacting to his partner's fear as he moved to shoot the figure next to the squad.

The officers had come to the alley that night after Ruszczyk called police concerned that someone outside her house was being attacked.

Noor told jurors that he and his partner, officer Matthew Harrity, sat in the squad in the alley and were about to clear the call and move on when they heard a bang.

After the noise, he said he saw Harrity, who was in the driver's seat, reach for his weapon, that Harrity struggled to get the weapon out and had fear in his eyes.

Noor, in the passenger seat, said he saw a blonde woman in a pink shirt raise her arm, and heard Harrity exclaim, "Oh, Jesus."

Noor said he put his left hand on Harrity's chest and extended his right arm to fire. He said at that moment he feared for his life "and there was a threat, and my intention was to stop the threat."

He added: "I fired once, and then the threat took a couple steps back."

Prosecutor Amy Sweasy pressed Noor about his decision to fire. Noor acknowledged that he didn't see Ruszczyk's hands before shooting. Asked if he knew he was shooting a person, Noor replied, "Yes, ma'am."

Two police use-of-force experts testified for the prosecution Wednesday, slamming Noor for firing in that situation. One said that "no reasonable police officer" would have perceived Ruszczyk as a threat that night, and that being startled doesn't justify deadly force.

On the stand, Noor pushed back on those criticisms. They "didn't look at the totality of the circumstance." Noor said repeatedly that his partner "feared for his life" and he could tell, despite Harrity never saying so.

Former Minneapolis police officer Mohamed Noor waits to go through security Thursday at the Hennepin County Government Center. Jim Mone | AP

Noor said he realized that Ruszczyk wasn't a threat when he got out of the squad vehicle and Harrity told him to put his gun away.

When Noor realized that Ruszczyk was dead, "It felt like my whole world came crashing down," he told the court.

He said he felt sad and traumatized in the shooting's aftermath.

"If I had known this would happen, I would never have been a cop," he said.

No longer on the force, Noor is charged with second- and third-degree murder and second-degree manslaughter in the killing of Ruszczyk, also known as Justine Damond, in July 2017.

She had called 911 to report what she thought was an assault happening behind her home. Investigators say Noor, one of the responding police officers, shot Ruszczyk through the open driver's side window of the squad as she approached.

Noor's defense attorneys have argued the officer fired to protect his terrified partner after hearing a thump on the squad and then seeing a figure by the driver's side window raising an arm.

Prosecutors, who've rested their case, say the thump was a story made up later and that Ruszczyk, approaching the squad in her pajamas, could not have been considered a threat.

Until taking the stand Thursday, Noor had declined to cooperate with investigators and hadn't spoken publicly about what happened that night.

Focus on training

Responding to questions from defense attorney Thomas Plunkett, Noor said he wanted to be a police officer to serve "the city of Minneapolis and the diverse communities there."

One of 10 kids, Noor moved from Somalia to a Kenya refugee camp at age 5, and then to the United States at age 7, first to Chicago, then south Minneapolis and New Hope. He said in court that he "fell in love with the city and wanted to make a difference."

Plunkett asked Noor about his training, focusing on use of force, anti-ambush and defensive training as a Minneapolis police cadet. The attorney noted a mistake Noor made where he left a live round in the gun. Noor said that other cadets made similar mistakes and shot the floor, ceiling or carpet.

Noor brought up a time at training when he was hit by a paintball. "The most important takeaway for me is actions are better than reactions," he said.

Asked Plunkett: "So the point is, if you don't do your job correctly, you get killed?"

Noor responded, "Yes, sir."

Ambush fear?

Noor broke down on the stand briefly when talking about the 1992 ambush killing of Minneapolis officer Jerry Haaf, which Noor heard about during his training.

Noor's attorneys have also suggested during the trial that Noor feared an ambush in the alley that night.

On Thursday, however, Plunkett was reprimanded by Judge Kathryn Quaintance again for getting into ambushes of police officers that happened.

"There's no indication of an ambush here," Quaintance said. Plunkett argued that was the perception that night of Noor's partner, officer Matthew Harrity, and that it plays into Noor's state of mind that night.

Noor's testimony Thursday could also open the door to having his Minneapolis police psychological exam entered as evidence in the trial.

Before the trial began, Quaintance ruled the exam would be excluded from trial but left open the possibility of reconsidering that ruling if Noor testified. The prosecution would have to ask her to reconsider.