A pounding on the police car led Minneapolis cop Mohamed Noor to believe he was being ambushed when he shot and killed Australian woman Justine Damond, according to a local news report.
The independent investigation into Saturday night's fatal shooting has revealed that when Noor and his colleague Matthew Harrity responded to a 911 call from Damond they were "startled by a loud sound" before Noor shot her.
Now, a two fresh accounts have shed new light on what spooked the officers.
Citing an anonymous source, the Minneapolis TV station KSTP reported that the officers were sent to the alley off Damond's home after she reported that a possible assault was under way.
When they failed to notice anything suspicious when patrolling the area in the police car, they were dispatched to another incident.
Before departing the scene, they saw a young man ride past on a bicycle.
As the officers watched the cyclist ride past on the passenger side of the vehicle, they were startled by a pounding on the driver's side, the source said.
The sound led the officers to believe they were "caught in an ambush", KSTP reported, and Noor fired his gun, which was in his lap at the time.
Breaking: Minneapolis Police have released 911 call transcript from Justine Ruszczyk reporting possible sex assault on night she was shot pic.twitter.com/r3a7UGiR0B
The bullet fired past Harrity in the driver's seat, through the open driver's side window and struck Damond in the abdomen.
The officers performed CPR on the 40-year-old until paramedics arrived but she died at the scene.
The KSTP report matches with an account of the shooting given by a friend of Noor, who said Damond "startled" him before he opened fire.
The friend told the Daily Mail that he and his colleague saw a panicked figure in the dark who rushed towards their vehicle, which was patrolling the area with its lights off. The figure, who they perceived to be a threat, turned out to be an unarmed Damond holding a mobile phone.
"Mohamed believes he acted to protect himself and his colleague, but accepts since that she was not armed," the unnamed friend said.
"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."
The friend also told the Mail that he felt he had been "thrown under the bus" by his police colleagues.
"His colleagues are accusing him of not showing proper police conduct on Saturday night," the friend said.
On Wednesday, Harrity's lawyer, Fred Bruno, backed the theory that the officers believed they were being ambushed.
"It's certainly reasonable to assume that any police officer would be concerned about a possible ambush under these circumstances," Bruno told Minneapolis's Star Tribune newspaper.
"It was only a few weeks ago when a female NYPD cop and mother of twins was executed in her car in a very similar scenario."
Bruno was referring to the case of police officer Miosotis Familia, who was patrolling New York's crime-ridden Bronx borough on July 5 in a police car when a mentally ill man walked up and shot her in the head through the passenger window.
Meanwhile, the anonymous source told KSTP that the mystery cyclist who was on the scene filmed the aftermath of the shooting - which would be a crucial piece of evidence if it exists.
However, the Bureau of Criminal Apprehension, which is investigating the killing, maintains that its investigators are not aware of any video or audio of the incident.
The bureau has asked for the cyclist, described as an 18- to 25-year-old caucasian, to come forward and tell investigators what he saw.
The KSTP report goes against the theory that the sound the officers heard on Saturday night was fireworks. This idea gained traction after an officer said during the police radio conversation after the shooting that "aerial fireworks" may have been let off in the area.
Noor has refused to be interviewed by investigators and the BCA has no legal power to force him to give evidence.
"We cannot compel officer Noor to make a statement," Minneapolis mayor Betsy Hodges told reporters on Tuesday.
"I wish we could."
Noor's family broke their silence on the case on Wednesday, implying the shooting was a tragic mistake.