Acting police Commissioner Shane Patton has confirmed there is no evidence the incident is connected to terrorism – however officials are still treating the incident as a “deliberate act”.
The 32-year-old suspect, who was the only person in the vehicle at the time of the incident, reportedly has a history of drug abuse and mental health problems.
Another man, age 24, was arrested while filming the incident but is not believed to have been connected.
He is alleged to have had knives in his bag.
Commissioner Patton said: “At this time we do not have any evidence for any intelligence to indicate there is a connection with terrorism.
“Having said that, however, we continue to support this investigation without counterterrorism command to ensure that there isn’t that connection and that there is no ongoing threat.”
Officials have confirmed 19 people are injured following the incident, with four sustaining critical injuries after the white SUV plugged into pedestrians.
A pre-school aged child who was rushed to the Royal Children’s Hospital is believed to be among those in a stable condition.
Commissioner Patton added: “I think to describe this as a lone wolf incident is not probably not apt.
“This is an horrific incident where a person drove directly at pedestrians.
“It is a crime and we will be fully exploring that… as I have said earlier, one of the key aspects we are exploring is in respect to mental health backgrounds and drug use in respect of this individual.
“We will work through that and see if there are any learnings.”
Witnesses said the white Suzuki SUV showed no signs of slowing as it mowed down crowds of people at the busy intersection near the corner of Flinders and Elizabeth streets.
One woman who saw the harrowing incident unfold said she heard screams before she saw “people flying everywhere”.
She added: “We could hear this noise, as we looked left, we saw this white car, it just mowed everybody down.
“People are flying everywhere. We heard thump, thump. People are running everywhere.”