Victoria Police believe yesterday's Flinders Street car rampage was not terror-related.
Two men were arrested at the scene, including 32-year-old Saeed Noori, who believed to have been behind the wheel and remains under police guard in hospital.
While the second man, a 24-year-old who was arrested at the scene has been released.
The 24-year-old is expected to be charged on summons with possess cannabis and possess controlled weapon.
These offences are not linked to the Flinders Street incident.
19 were injured when a white Suzuki SUV mowed down pedestrians on the packed intersection of Flinders and Elizabeth Streets at 4.41pm on Thursday.
Of the 19 people injured - four are critical on Friday morning, while a four-year-old boy has head injuries and is in a stable condition.
On Friday morning police were yet to formally interview Noori as he remains in hospital.