Police have vowed to solve the double murder, after the women, aged 39 and 48, were killed when a hail of bullets was fired at their vehicle in Panania on Saturday night.
"This is an appalling attack on two women, who lost their lives in a planned murder and assassination really, that's happened in a public street in Sydney," Homicide Squad Commander, Detective Superintendent Danny Doherty told media on Sunday.
"It's not acceptable by any standards. It's unprecedented, really, and we're determined to get the answers for the family."
Emergency services were called to a street in Revesby just before 8.50pm on Saturday, following reports of a shooting.
The 48-year-old, identified only as a mother of two, could not be revived and died at the scene. The 39-year-old was taken to Liverpool Hospital in a critical condition, where she later died.
A girl, 16, and man, 20, were also in the car at the time and were left incredibly shaken but physically unhurt, Det Supt Doherty said.
He said they were incredibly lucky not to have been killed or seriously injured.
Police believe the shooting occurred at Hendy Avenue, Panania, before the vehicle travelled to Weston St, Revesby, where emergency services were contacted, Det Supt Doherty said.
Police located burned out cars in nearby suburbs in the hours following the attack, in Revesby, Yagoona and Moorebank, and are investigating if the vehicles are linked to the shooting.
"These are the hallmarks of a planned attack. It was methodical. It was planned," Det Supt Doherty said.
He said he could not identify the victims because police were still in the process of contacting relatives, who he described as devastated.
Police were familiar with the 48-year-old victim for having past connections to figures well-known to police, and one theory is that she may have been the target.
Det Supt Doherty said the three other people in the vehicle had no links to organised crime.
He urged the public to come forward with information about the attack.
"We're determined to get the answers, but the only way we can do this is to get help from the public," Det Supt Doherty said.
"The time is now. This is unprecedented."
He urged people to have compassion for the victims, and not to speculate about their involvement with organised crime.
"We should be asking questions, how could this happen? How did we get to this point, where two women have lost their lives in Sydney, in a public street?"
Det Supt Doherty said underworld figures used to operate by "unwritten laws" where women and children were protected from being attacked - a rule he no longer believed applied.
"I think this has just demonstrated how low they've got at this point, where any person that may be associated with someone who they want to target ... they don't discriminate, whether you're male or female," he said.
"The rule books have been thrown out the window."
Strike Force Laurantus has been established to investigate the incident.
Anyone who may have information, dashcam or CCTV from the surrounding areas is urged to contact Crime Stoppers on 1800 333 000.
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