Sutherland police area command Superintendent Donald Faulds said a number of bystanders, unaware of the situation, stopped to help.
Among them was Cronulla Sharks chairman Steve Mace, who recounted the terrifying moment he attempted to help the victim from her alleged attacker.
Mace was driving his son to junior football when the accident unfolded in front of him and when he got out to assist, he found himself caught in the attack.
“There was an accident in front of us,” Mace said. “I said to [his son] Cooper, ‘it looks like the airbags have gone off. I’ll quickly jump out to make sure they’re OK’.
“I could hear him [the attacker] screaming, but I could hear her screaming more. I ran around to the other side and he was just ruthlessly stabbing her. She was in the car with the seatbelt on. I’m trying to drag her out between him trying to stab me.”