Peter Smith was just 20 years old when he died after being punched in the head at a milk bar in Sydney's Pitt Street.
For 43 years, his sisters believed Peter died of a burst aneurysm, which had been a ticking timebomb in his brain since birth.
But in 2014, that all changed.
Belinda Stapleton, who was just four years old when her brother died, applied to access the Coroner's report and was "absolutely stunned" to learn her brother never had a brain aneurysm.
"We knew we had to do something," she said.
What ensued was a five-year fight by Ms Stapleton and her sisters Judy Smith and Pamela Budai to discover what really happened to their brother and whether it was properly investigated.
Their fight will culminate in a NSW Coronial inquest into Mr Smith's death, starting on Tuesday — almost 48 years to the day since he died on October 22, 1971.
Ms Stapleton said she was told by their parents that Peter died from the aneurysm, but his best friend had told the family about the punch.
The pair had gone drinking at a pub in the city that Friday night, when they decided to buy snacks at a nearby milk bar.
Peter was allegedly pushed, then punched in the head before falling to the ground. He died almost immediately.
"We knew the story of the punch … but figured the punch would have triggered the aneurysm, which would have ruptured at some point anyway," Ms Stapleton said.
But still, questions about her brother's death remained.
"It was constantly nagging at my sister and me. We needed to find out what had happened — the curiosity, the need to know never stopped."
Police found 'no suspicious circumstances'
Following the shocking revelations of the coroner's report, the sisters approached their brother's best friend and discovered he had not been formally interviewed by police.
Instead, their uncle, who was a senior police officer at Chatswood at the time, took a statement from him over the phone. That statement was never passed on to the investigating officer.
It was a further blow to discover the investigating officer's report to the coroner was signed off just a day after the death, citing "no suspicious circumstances".
Despite the setbacks, the sisters' quest for answers took a giant leap in 2015, when they attended a lecture by Hadyn Green, a forensics specialist and retired police superintendent who helped identify victims of the 2004 Thailand tsunami.
Mr Green offered to examine the information they had gathered on their brother's death and wrote a report which concluded that the police investigation was inadequate and their uncle's involvement had interfered with the process.
The sisters also obtained a report from a neuropathologist which supported the theory that Peter died from an assault.
With this newfound information, they applied for an inquest in 2016 and a year later were told the Coroner would hear the case.
"We have been repeatedly told by members of the legal profession how amazing it is that we have got this far," Ms Stapleton said.
"We just want the story heard in honour of Peter."
Police have tracked down the original investigating officer.
He will be questioned during the inquest, as will the milk bar owner.
Ms Stapleton said she hoped the inquest would correct the record on Peter's cause of death and give his best friend the chance to "finally tell the story that has haunted him — and us — for so many years".
