No one has ever been arrested for Mary Anne Fagan's death but there are hopes a $1 million reward on offer could finally provide some clues to her five children.
Her youngest son, Patrick, feels they are the cusp of understanding what happened and has pleaded for anyone with any information to finally come forward.
Patrick Fagan was a baby when his mother was murdered at their home 46 years ago. (Con Chronis/AAP PHOTOS)
"Please, understand that what difference it would make to me and my family to to give us this justice," Mr Fagan told reporters on Friday.
"If you know something, it doesn't mean anything to you now, so please just give us the information."
Ms Fagan was last seen alive at her home in Armadale, in Melbourne's south east, Â at 10.30am February 17, 1978, after driving four of her children to school.
She had a brief phone conversation with her husband, who was away at a work function, at 11am.
Later that day the children, aged 15, 13, 12 and six, realised something was wrong when they came home to find the side gate open, her car in the driveway and the house locked.
They broke a window to get in, finding Patrick crying inside and their mother dead in the front bedroom. She had been bound, gagged and stabbed several times.
Investigators have never established a motive for her death but are confident someone knows what happened, Victoria Police Homicide Squad Detective Inspector Dean Thomas said.
"I've no doubt that the person or persons responsible have confided in other people, and there will be people out there that know what has happened," he said.
"So I implore anybody out there, now is the time to come forward and share that information with us."
On Friday, Victoria Police announced a $1 million reward for information to catch and convict those responsible.
Detective Inspector Dean Thomas implored anyone with information about the crime to come forward. (Con Chronis/AAP PHOTOS)
Indemnification from prosecution will also be considered for anyone who provides information about the main offender or group of offenders.
Mr Fagan said his father shielded his five children from the search for the killer or killers but died without knowing what happened to his wife.
He has no memories of his mother's death and has instead been forced to stitch together an idea of what she was like from stories and her clothing.
"Obviously it's horrendous," he said.
"There's multiple facets of how horrible it is from the point of view of what mum had to go through to what somebody could be thinking to do an act like that."
Inspector Dean Thomas said detectives are keeping an open mind about what happened, noting she lived on Dandenong Road which is very busy.
Many people were interviewed, including a construction crew doing repairs to the road outside her house, but no weapon was ever found or suspect identified.
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