The man arrested over the Melbourne attack was filmed videobombing a Nine News reporter's live cross before he allegedly mowed into crowds of people.
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Three people - an infant and a man and a woman aged in their thirties - were killed in the incident on one of Melbourne's busiest shopping strips and 15 others are in hospital.
Hours before the attack, the man was filmed waving his cap out his car window in the background of a reporter's live cross about an earlier incident involving him.
He is alleged to have stabbed his brother earlier on Friday before going on a deadly rampage down a Melbourne CBD street in the afternoon.
It's believed he was driving the same car that he would later use in the attack.
Police say the man does not have any affiliations to a terror group but has a history of family violence and mental health issues.
Among the injured are four children, including one who is in a critical condition.