It started when two carloads of men passed each other on a speed hump in a car park in Sydney's north-west.

Sydney father David Campbell, 26, believed the people inside a Nissan Skyline had given him a "death stare".

David Campbell was fatally stabbed during a road rage fight in February 2015.

His friend Scott Wilson tried to calm him down and said, "Let's just go."

Mr Campbell decided to do a U-turn and followed the Skyline back into the Macquarie Park car park, along the Hawkesbury River.