The police officer who killed an Australian woman who approached his car in her pyjamas has explained what caused him to shoot.

Officer Mohamed Noor claims he was “startled” by bride-to-be Justine Damond before he opened fire through the window of the vehicle when it was parked near her home in Minneapolis.

A friend of the killer cop, who has been suspended by Minneapolis Police Department, told DailyMail.com that he reacted after seeing a figure emerge from the dark running towards him.

Justine Damond was killed in her pyjamas when she approached the police car (AP)

The friend said: “Mohamed believes he acted to protect himself and his colleague, but accepts since that she was not armed.

“It was over in seconds and it was a very tense moment. He is sorry for the woman and her family.

“But he would never have opened fire without genuinely feeling in danger.”

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The friend added that Noor feel he has been “thrown under the bus” by his colleagues, adding: “His colleagues are accusing him of not showing proper police conduct on Saturday night.”

Noor shot Ms Damond, who had phoned police to report a possible sexual assault, once in the abdomen and she was pronounced dead at the scene.

Her fiancee, Don Damond, has described her death as a “homicide” and is demanding a federal investigation into her death.

Family and friends gather on Sydney’s Freshwater Beach to throw flowers into the sea in memory of Justine (AP)

Noor and the second officer in the cars did not turn on their body cameras until after the shooting, and the squad car camera was also not activated.

The Minnesota Bureau of Criminal Apprehension said forensic testing is being completed and evidence is still being examined before possible charges are brought.

Top pic: AP