Victoria Police could face civil action after an inquest found major investigative blunders in the murder of Maria James, but could not identify her killer.
Ms James was stabbed 68 times in June 1980 at her Thornbury home and bookshop in Melbourne.
Coroner Caitlin English said two now-deceased men - Catholic priest Anthony Bongiorno and Peter Keogh - remained significant persons of interest following the 17-day inquest.
Mark James believes the priest killed his mum and says the inquest's open finding is a "disappointing blow".
"We've been trying to get justice for our mum for many years and we were hopeful that we'd get some definitive answers through the coronial process - we haven't yet," he told reporters outside the Victorian Coroners Court on Thursday.
"The findings handed down today have failed to name the person, or persons, responsible for taking our mum away from us in the cruellest way."
Ms English said while police were flooded with information and false leads following a $50,000 reward at the time of the 38-year-old mother-of-two's murder, they were responsible for major errors which hamstrung the investigation.
The most significant mistake was the use of a bloodstained pillowcase in 2003 - initially thought to be from Ms James' home - to rule out a handful of key suspects.
In 2017, it was revealed the item was from an unrelated case, which counsel assisting the coroner, Sharon Lacy, said cost "14 years of potential progress".
Meanwhile, a quilted bedspread from the crime scene was recovered in June last year.
But other items of evidence, including Ms James' bloodstained clothes, have long been missing from the police exhibits.
"It is remarkable that these errors all occurred for different reasons and were not connected," Ms English said.
Mark James indicated he and his brother were considering taking civil action against the police over their failure to preserve evidence.
"This is not good enough and we feel there should be ramifications because this has played a significant role in us being denied justice," he said.
"No victim of crime, or their loved ones, should be denied justice because of mistakes or failures of police."
Mr James remains certain Father Bongiorno, who was accused of sexually abusing his brother, murdered his mum and wants the priest's body exhumed for further examination.
"It's clear to us, and to many others, that priest killed our mum, yet he appears to have gotten away with it," Mr James said.
Ms English said Keogh, who was known to "hate women", lived in the area and worked night shifts could have been at the bookshop when Ms James was murdered about midday.
But the coroner found police quickly eliminated him as a suspect "without proper grounds".
She also noted that the boyfriend of Vicki Cleary, whom Keogh stabbed to death in 1987, recalled him threatening her: "I'll do to you what I did to the bookshop woman."
But Mark James believes Keogh had nothing to do with his mum's death.
"Most of the scuttlebutt about Keogh can be traced back to himself," he said.
"He was a ruthless monster who liked boasting."
Adam James said he and his brother would never give up trying to get justice for their mother.
"We love her and miss her every day," he said.
Ms English recommended police do a full search for missing evidence.
She also said inquiries should continue into Father Bongiorno and Keogh, who both had "opportunity" to kill Ms James.
An investigation into the unsolved murder remains ongoing with DNA from 11 human hairs from the quilt set to be examined.
