The horror of the carnage that also injured dozens more was heard in the police radio played during the first day of an inquest into the rampage.

"This car is a danger to pedestrians and is in the middle of the Flinders and Swanson street doing donuts," one officer warns.

Gargasoulas was tailed by police for hours on January 20, 2017 before driving a stolen car through the CBD and mowing down dozens of pedestrians. He was eventually shot and tasered after his car came to a halt.

Police transmissions detail attempts to catch the man they described as being in "maniacal psychotic state" and threatening to kill people.

Victims' families say police and authorities had countless warnings before Gargasoulas killed their loved ones.

Melinda Tan told the inquest police and other authorities had "many red flags and opportunities" to stop his murderous rampage.

She said police were never in control of the situation, in which her husband Matthew Si, 33, was killed.

"The offender played them and he won," she said.

She questioned how the force was unable to stop one person in a car despite ample resources at their disposal.

Ms Tan also said the decision that allowed Gargasoulas to get bail six days before the massacre was flawed.

Baby Zachary Bryant's mother, Nawwar Hassan-Bryant, said it was unfair her "handsome, beautiful little man" was robbed of his life at just three months.

"The last memory we have with him is taking him off his life support and feeling his heart beat for the last time," she said.

Zachary's father said there were numerous chances to stop Gargasoulas.

"This crime was the result of one man, but the system is also complicit in our son's death," he said.

Police radio communications were played of the moments before the pedestrians were mowed down.

They warn the driver is armed with a knife, having just stabbed his brother, and very dangerous.

Seconds later, a frantic voice adds: "Someone needs to take this vehicle out before he kills someone."

In the following seconds, an officer says: "We have someone down on - multiple victims. Many units as involved as you can. We need to take him out."

Gargasoulas had told a friend: "I'm going to do something drastic, take everyone out, they can suffer the consequences. Watch me, you'll see me tonight on the new. The police have stopped me before but they ain't gonna get me this time. I'll make you believe me."

There were unsuccessful attempts by multiple police units to track and pursue Gargasoulas across several suburbs as he drove erratically and evaded police, who at one stage were just five metres away from him.

Coroner Jacqui Hawkins said the inquest would examine how a recidivist criminal who had shown extreme violence was able to murder six innocent people and seriously injure scores of others.

The victims included baby Zachary and 10-year-old Thalia Hakin, along with Mr Si, Jess Mudie, 22, Yosuke Kanno, 25, and Bhavita Patel, 33.

Gargasoulas, who suffers paranoid schizophrenia, was jailed in February for at least 46 years.

Australian Associated Press