Dimitrious Gargasoulas has been named as the man police believe is responsible for deliberately driving a maroon coloured Holden car into the crowd in Bourke Street and Queen's Street in the city centre.
These are the first pictures of the 26-year-old suspect just before he was seen ploughing into shoppers and lunchtime workers, killing three, including a man and a woman in their 30s and a young child.
At least 25 people are thought to have been injured.
The driver has been named as Greek Australian Dimitrious Gargasoulas, 26
The suspect, who was known to police, can be seen hanging out of the car's window as he appears to be screaming at pedestrians, moments before he drove into the pedestrianised shopping area.
Police arrested him nearly an hour later after reports of shots being fired and person being pulled from a car by police on William Street.
Detectives said the situation had been "contained" and the incident was not terror related.
On a Facebook page appearing to belong to Gargasoulas, he continually referred to "you dogs" and in one said: "I know exactly how to take you DOGS down the power of knowing has revealed and i shall have GODS law re-instated [sic."
The suspect's car was seen smashed into a pole
A post from Dimitrious Gargasoulas' Facebook page says he is a Greek Islamic Kurd
In another post, he claimed to be a "Greek Islamic Kurdish Angel of Cult".
And in one post, he took sympathy with "cop killers", saying: "The next time you hear of a police officer being killed “in the line of duty,” take a moment to consider the very real possibility that maybe in that case, the “law enforcer” was the bad guy and the “cop killer” was the good guy.
"As it happens, that has been the case more often than not throughout human history.
"F*** da police xoxoxo."
A child was killed and another infant is in critical condition in hospital
Victoria Police's Chief Commissioner Graham Ashton confirmed the arrested man is well-known to the police.
Mr Ashton said the man had no links to terrorist activity but had an extensive criminal history linked to family violence.
He said: “He has come to our attention on many occasions in the past.
“That is mainly linked to drug issues and mental health problems.
“He also came into our attention in recent days in relation to assaults and was charged by us last weekend.”
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Police had been chasing his car following a stabbing in the nearby Windsor district before he crashed into the pedestrian area.
A Victoria Police statement, said: “Police shot the man who was the sole occupant of the vehicle and he received bullet wounds.
“Police understand the incident is linked to a stabbing that took place in Windsor early this morning (20 January) involving parties known to one another.”
“Following this incident, it is alleged the same man took a woman, who is known to him, hostage in his car.
“She managed to escape from the car on the Bolte Bridge earlier today.”