The sister of a woman brutally slain in her Collingwood home in an infamous double murder has issued an emotional plea for help in solving the case.
After a 40-year hunt sifting through more than 130 possible suspects, police believe they may be closing in on the killer in the Easey Street murder case.
Homicide squad detectives have announced a $1 million reward for information on the frenzied stabbing murder of two women in Collingwood in 1977.
The bodies of 28-year-old Suzanne Armstrong and 27-year-old Susan Bartlett were discovered with multiple stab wounds on January 13, three days after their killings at their Easey Street home .
Ms Armstrong's 16-month-old son, Gregory, had been left unharmed in his cot and was found with the bodies after neighbours heard his crying.
The killer sexually assaulted Ms Armstrong in her bedroom and stabbed her 29 times, also attacking Ms Bartlett and stabbing her 55 times before leaving her body in a pool of blood in the hallway.
DNA testing has been used to eliminate a number of suspects and remains a central part of the investigation.
Ms Armstrong's sister Gayle said the family has tried its best to move on, but the murder changed their lives forever.
"It's half a lifetime that we've lost," she said.
"It's something that has to be finalised and this reward should have been offered 39 years ago."
Gayle, who went on to raise Gregory as her own son, said her sister was meant to be with her in Hungerford in outback Queensland at the time of the murder but hadn't been able to find someone to mind Gregory.
She expressed frustration at the initial investigation into the murder, however praised the work of the cold case homicide team now examining the case.
"We weren't even interviewed," she said. "We had to make an appointment to go down to the police station to talk to the police which was pretty bad."
Homicide squad detective inspector Michael Hughes said he hopes the $1 million reward announced on Sunday would encourage someone who might know about the murders to step forward.
"We believe after 40 years someone out there knows something and it is time for them to come forward," he said.
"These unsolved murders have been extremely devastating on these two young women's families and after all this time we would like to provide them with closure."
Insp Hughes said detectives have been actively working on a list of 130 people of interest, of which 41 are deceased.
He said police are confident that if the offender is one of the 130 he will eventually be caught.
"I don't believe you can commit a crime of this brutality and go unnoticed by police, so I think technology will catch up with him and our investigation will catch up with him," he said.
"I think it's a terrible crime, it's one of our worst in Victoria."
Anyone with fresh information about the murders is urged to contact Crime Stoppers on 1800 333 000 or visit www.crimestoppers.com.au.