A Minneapolis cop who shot dead an Australian yoga teacher in her pajamas after he answered her 911 call has been charged with murder.

Officer Mohamed Noor turned himself in Tuesday morning and is being held on murder and manslaughter charges for gunning down 40-year-old Justine Ruszczyk Damond on July 15 while she was engaged to be married.

He shot Damond in the stomach when she approached his squad car minutes after she called 911 to report a possible sexual assault in the alley behind her home.

Officer Mohamed Noor (right, in a police mug shot released today) turned himself in Tuesday morning and is held on murder and manslaughter charges for shooting 40-year-old life coach Justine Ruszczyk Damond (left) on July 15 while she was engaged to be married

Damond's family said in a written statement they are pleased that Hennepin County Attorney Mike Freeman decided to bring charges of third-degree murder and second-degree manslaughter.

They say they hope a strong case will be presented and Noor will be convicted.

Their statement says justice 'demands accountability for those responsible for recklessly killing the fellow citizens they are sworn to protect'.

A statement from the Ruszczyk and her fiance, Don Damond, said: 'While we waited over eight months to come to this point, we are pleased with the way a grand jury and County Attorney Mike Freeman appear to have been diligent and thorough in investigating and ultimately determining that these charges are justified.'

Damond was unarmed and had called 911 caller to alert police to what she believed may have been a rape taking place in the alley behind her home.

Noor told friends he was 'startled' by his victim seconds before he opened fire.

Speaking on the condition of anonymity, one friend said the officer had opened fire when an unidentified figure emerged from the dark and ran towards the vehicle.

Noor poses for a file photo taken by the Minneapolis Police Department in May 2016

The officer said he was not sure what the person was carrying and momentarily opened fire through his driver-partner's open window.

It was confirmed that Damond's cell phone was found alongside her during the tragedy.

Noor told associates it was dark and the situation was already tense as the caller had been 'panicking' when making the 911 call reporting an assault in the alley beyond where Damond lived with her fiancé and his son.

The squad car, driven by his partner Matthew Harrity traveled hastily down the unlit alley between Washburn and Xerxes avenues south from West 50th Street toward West 51st Street.

Neither officer's body camera was switched on, and there is no video of the shooting.

Crucially, the vehicle did not have its lights on and this may have been so as not to give any suspect notice that police had arrived and buy precious time to apprehend the target. That the car was unlit was disclosed by Harrity to the BCA.

Both Noor and the BCA's version of events agreed on the car's lights being off.

Mrs Damond with her fiance, Don, seen together in an undated photo posted on Facebook

Aftermath: Cops closed down the area around the shooting but lack crucial bodycam evidence because neither Noor or Harrity activated theirs, in breach of regulations

According to Noor's version when they reached the end of the alley, they came across a waiting, panicking figure.

It was dark, and the figure was moving around and approached their vehicle.

Noor said he did not know whether the figure who rushed towards their vehicle was the 911 caller or even if it was a man or woman.

He his weapon through Harrity's open driver's window hitting his victim once in the abdomen.

Both he and Harrity gave CPR to the victim before help and back up arrived, but she was pronounced dead at the scene.

The charge of third-degree murder carries a maximum of of 25 years in prison, although the presumptive sentence is 12 years.

The second-degree manslaughter charge carries a maximum of 10 years in prison, and the presumptive sentence is four years.

Noor's bail is set at $500,000, according to jail records.

Johanna Morrow plays the didgeridoo during a memorial service for Damond at Lake Harriet in Minneapolis on August 11

The 'twin cities' of Minneapolis and St Paul have been rocked in recent years by police shootings, putting the community and law enforcement on edge.

Last month a police officer was acquitted after he shot Philando Castile during a traffic stop while Castile's girlfriend live streamed the horrifying incident.

Violent protests also erupted after two officers fatally shot 24-year-old Jamar Clark in 2015 and were not charged.