Akiir Muo, the woman who James Gargasoulas took hostage before going on his murderous rampage, wept and wailed uncontrollably when she found out her killer boyfriend had mown down pedestrians in Melbourne's CBD.

Key points: A coronial inquest inquest has heard a tape recording of the moment Ms Muo learned of Gargasoulas's fatal rampage

A coronial inquest inquest has heard a tape recording of the moment Ms Muo learned of Gargasoulas's fatal rampage Gargasoulas had previously told her twice he would "run everyone down in the city"

Gargasoulas had previously told her twice he would "run everyone down in the city" The detective who gave Ms Muo the news said he believed her reaction was genuine

The Bourke Street coronial inquest has been played distressing audio of the moment Ms Muo learnt that Gargasoulas had carried out the threat he had made to her just hours before he went on a killing spree on January 20, 2017.

Shortly after 7:00pm, about five-and-a-half hours after the massacre, police officer Lachlan Watson, who was then a Detective Senior Constable with the Homicide Squad, took Ms Muo to a McDonald's drive-through following her police interview.

James Gargasoulas killed six people and injured 27 others when he drove into pedestrians on Bourke Street three years ago. ( AAP: Stefan Postles )

After ordering a large Big Mac and Double Quarter Pounder meal, Ms Muo asks Senior Constable Watson whether "Jimmy" was arrested.

He confirms this, and then she asks how long Gargasoulas will go to prison for.

Senior Constable Watson: It'll be a long time. Yeah, a very, very long time. I'm sure by now you've, you know what he's done. Ms Muo: He's just stabbed his brother. Senior Constable Watson: Oh, so you don't know about the second part, about what he did after? Ms Muo: Nah.. Senior Constable Watson: Really? All right. Well then we're going to have to have a conversation and I'll have to tell you about what he's done.

Senior Constable Watson then turns the corner and parks the car, before breaking the news to Ms Muo as their food begins to cool.

Senior Constable Watson: He did exactly what he told you. He ran people over. Ms Muo: Did he? Senior Constable Watson: Yeah. Yeah. There's three or four people dead. Ms Muo: Oh my God. Senior Constable Watson: There's three people dead and there's another one that's pretty close to dead. Ms Muo: Oh my God.

At this point Ms Muo, who earlier appeared on footage recorded during a separate police interview wrapped in a green blanket, begins to sob and wail.

Ms Muo: Why did Jimmy do that for? Were they adults that he ran over or just were kids? Senior Constable Watson: Well… Ms Muo: Oh, God…

Earlier that same day, and shortly after he had stabbed his brother, Gargasoulas had taken Ms Muo hostage and the pair went to someone's house.

The badly damaged car driven by Gargasoulas down Bourke Street. ( ABC News )

She was woken by Gargasoulas, who flew into a rage after police called her phone.

"If the cops come and find me, I'll run everyone down in the city," he told her.

Later, under Melbourne's West Gate Bridge, he repeats this threat before pushing her from the car: "I swear if they catch up to me I'm gonna run everyone down in the city."

Bourke Street victims: Yosuke Kanno: 25-year-old student from Japan. He had just been to lunch with a friend when he was struck

25-year-old student from Japan. He had just been to lunch with a friend when he was struck Jessica Mudie: 22-year-old insurance consultant from Sydney who was in Melbourne for a business meeting. She was returning from lunch with colleagues.

22-year-old insurance consultant from Sydney who was in Melbourne for a business meeting. She was returning from lunch with colleagues. Matthew Poh Chuan Si: 33-year-old architect and father of an 18-month-old daughter. He had just been to lunch with his wife.

33-year-old architect and father of an 18-month-old daughter. He had just been to lunch with his wife. Bhavita Patel: 33-year-old accountant. She had been to lunch with colleagues.

33-year-old accountant. She had been to lunch with colleagues. Thalia Hakin: 10-year-old primary school student. She was on her way to a circus show with her mother and sister.

10-year-old primary school student. She was on her way to a circus show with her mother and sister. Zachary Matthew-Bryant: The 3-month-old was in a pram with his sister when he was struck.

According to Victoria Police's own internal report, dubbed the Fontana Review, Ms Muo said that police then asked her where Gargasoulas was going.

"He was going to Werribee and then he was going to the city to run people over," she told them.

Ms Muo was taken into custody before midday but was not interviewed by police until after 2:00pm, about half an hour after Gargasoulas turned onto Bourke Street, killing six people and injuring 27.

Families members of the six victims were warned about the distressing nature of the recording before it was played to the inquiry.

Mr Watson, now a sergeant with Victoria Police, was asked by counsel-assisting the inquest, Paul Lawrie, whether he believed Ms Muo's reaction was genuine.

"No doubt. That was the first time she heard it," Sergeant Watson replied.

"You can hear it. It was excruciating."

Ms Muo was due to appear before the inquest, but the Coroners Court was unable to find her.