It's possible that the sound was fireworks in the area.
The police officer who shot yoga instructor Justine Damond may have been startled by a loud noise before he fatally shot her, according to a preliminary investigation.
Read: Newly Revealed Audio Sheds Light on Final Moments of Yoga Teacher Shot Dead by Cop
The 40-year-old bride-to-be was in her pajamas when she twice called 911 to report a possible sexual assault in an alleyway near her home.
Officer Mohammed Noor was in the passenger seat of the cop car when he and a fellow officer arrived at the scene, moments before firing at least two shots at the woman.
The Bureau of Criminal Apprehension claims the squad car came to the alleyway and the officers were startled by a sound as Justine approached the driver side window.
A published report says the sound maybe have been someone banging on the vehicle. Another theory is that the sound they heard was fireworks, since police radio traffic earlier that night mentioned fireworks had been mistaken for gunfire.
Noor is reportedly not cooperating with investigators and Australia, where Damond is from, is looking for answers.
"This is a shocking killing," Prime Minister Malcolm Turnbull said. "It is inexplicable."
Read: Fiance Speaks Out After Cop Kills Minneapolis Yoga Teacher: 'Our Hearts Are Broken'
Meanwhile, a transcript has been released that details Damond's two calls to police that night:
Justine: “I can hear someone out the back and I’m not sure if she's having sex or being raped...I think she just yelled out, 'Help.'"
911 Operator: “You're just hearing a female screaming then?”
Justine: “I think she tried to say help and it sounds distressed.”
Eight minutes later, she called again.
911 Operator: “You're hearing a female screaming?”
Justine: “Yes, along behind the house.”
911 Operator: “Officers are on the way.”
Justine’s family and friends held a vigil on a Sydney beach before tossing flowers into the ocean.
Watch: Yoga Instructor to Wed Next Month Is Killed by Cops After Calling 911
