Prosecutors in the case of a former Minneapolis police officer who shot and killed Australian woman Justine Damond Ruszczyk are seeking to charge him with a more serious murder count, alleging he intended to cause her death.

Key points: Mohamed Noor is scheduled to face trial in April 2019

Mohamed Noor is scheduled to face trial in April 2019 The former police officer has refused to speak to investigators

The former police officer has refused to speak to investigators Ms Damond Ruszczyk's father has filed a $US50 million civil rights lawsuit

In a court filing, prosecutors said they want to charge Mohamed Noor with intentional second-degree murder over the July 15, 2017 death of Ms Damond Ruszczyk.

Authorities said Mr Noor shot Ms Damond Ruszczyk after she called 911 to report a possible sexual assault in the alley behind her home.

Mr Noor is already charged with third-degree murder and manslaughter.

In their request to add the second-degree murder count, prosecutors said the evidence showed Mr Noor intended to kill Ms Damond Ruszczyk when he aimed and fired at her.

"A person acts with the intent to kill not just when they have the purpose of causing death, but also when they believe that their act, if successful, will result in death," prosecutors wrote.

"As a trained police officer, the defendant was fully aware that such a shot would kill Ms Ruszczyk, a result he clearly intended."

Minnesota rules allow criminal complaints to be amended before trial. It will be up to a judge to grant the request.

Mr Noor is scheduled to face trial in April next year.

Peter Wold, one of Mr Noor's lawyers, said he had not seen any new evidence since Mr Noor was initially charged.

When asked if an additional count would postpone trial, he said he doubted it, adding: "We're ready."

Prosecutors say Mohamed Noor intended to kill Ms Damond Ruszczyk. ( Supplied: Hennepin County Sheriff's Office )

Prosecutors wrote in their filing that it would be up to a jury to weigh which degree of homicide, if any, was proven beyond a reasonable doubt.

Ms Damond Ruszczyk was a 40-year-old life coach and dual Australian–US citizen who had been living in Minnesota for more than two years.

Mr Noor was in the passenger seat of a squad car when he reached across his partner and fired at Ms Damond Ruszczyk through the driver's window after she walked up to them in the darkness.

Mr Noor has declined to speak with investigators.

But his partner, Matthew Harrity, told them they "got spooked" when Ms Damond Ruszczyk approached.

Mr Noor's lawyers had argued he acted reasonably because he feared he was in danger.

A lawyer for Ms Damond Ruszczyk's family said the additional charge would likely be allowed.

"It may well have been provoked by [Mr] Noor's defence team's admission of [Mr] Noor's 'intent', previously unknown to the prosecutor or the public because of [Mr] Noor's refusal to speak," he said.

"It doubles the recommended sentence under the sentencing guidelines for [Mr] Noor if convicted. Such charges often are a catalyst for pleas to the lower charges to avoid the longer sentence."

Ms Damond Ruszczyk's father, John Ruszczyk, has filed a $US50 million civil rights lawsuit against Mr Noor, the city and others.

That case has been put on hold while the criminal case proceeds.

ABC/AP