Mona Lisa Smith,16, a Murrawarri and Kunja girl, and Jacinta Rose "Cindy" Smith, 15, a Wangkumara girl, died in the early hours of December 6, 1987.
The vehicle they were travelling in rolled on the Mitchell Highway, between Bourke and Enngonia in outback NSW.
At the wheel was non-Indigenous then 40-year-old man, Alexander Grant, who had picked the girls up after offering them a lift home.
The coroner said the girls' families had been vindicated despite being repeatedly dismissed. (HANDOUT/NATIONAL JUSTICE PROJECT)
Instead of taking them there, he "plied" them with alcohol before taking them out onto the highway, a coronial inquiry concluded on Tuesday.
Following the crash, in which the girls suffered non-survivable internal injuries, evidence suggested a mostly uninjured Grant "horrifyingly" sexually interfered with an already dead Cindy.
The cause of the crash was accepted to have been a combination of, "intoxication, fatigue, road speed and a lack of lighting".
In delivering the findings 36 years after the girls' deaths, NSW State Coroner Teresa O'Sullivan said their families had been vindicated in pushing for answers despite being repeatedly dismissed.
She found the initial police investigation suffered from "very serious deficiencies" impacting the likelihood of any future criminal conviction, including failing to collect key evidence from the crime scene.
"Although it scarcely needs to be said, the conduct of Mr Grant was predatory and disgraceful," Ms O'Sullivan said.
"The uncomfortable truth, to my mind, is that had two white teenage girls died in the same circumstances, I cannot conceive of there being such a manifestly deficient police investigation into the circumstances of their deaths."
Grant, who died in 2017, was acquitted of driving-related offences relating to the incident during a 1990 criminal trial.
Despite welcoming the findings, family members expressed dismay no one would be held accountable. (HANDOUT/NATIONAL JUSTICE PROJECT)
A further charge of indecently interfering with a corpse was dropped before the trial due to difficulties with establishing the timing of Cindy's death based on the available evidence.
Despite welcoming the inquiry and it's findings, the girls' family members expressed dismay that no one would be held accountable, due largely to the racist attitudes of police.
"We hope that the police and others take away from this inquest how important it is to listen to Aboriginal people and Aboriginal families, particularly when we are talking about our children and our experiences," Cindy's sister Kerrie said.
"If only we had been listened to 36 years ago, we wouldn't be fighting now, and we could have seen someone held accountable."
Ms O'Sullivan accepted acute tensions existed between law enforcement and the Aboriginal community at the time and that racial bias had impacted the investigation into the girls' deaths.
Among several recommendations, Ms O'Sullivan said police should receive training about the cultural perspectives and ongoing impact of colonisation on Aboriginal people.
About a fortnight before the fatal crash, a man accepted by the inquiry based on the circumstances to have been Grant, picked up two other teen girls who were cousins of Mona and Cindy.
Grant bought the girls beer, allowed one of them to drive his car and propositioned them for sex which they refused, before he dropped them back near their homes.
Ms O'Sullivan found on the night he picked up Mona and Cindy, Grant was again "scoping the Bourke township for young girls to ply with alcohol and to sexually proposition".
Investigators initially believed Grant's account that Mona had been the one driving his Toyota 4WD ute, despite the vehicle having a manual transmission - which she did not know how to use.
Ms O'Sullivan acknowledged there were individual officers who did their very best to investigate the matter before Grant's criminal trial.
"Despite the best efforts of those officers, the failures in the hours, days and weeks following the accident ... had an irreparable impact on the investigation," Ms O'Sullivan said.
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