The sister of a woman raped and stabbed to death in a Melbourne home 40 years ago has criticised the way police initially handled her sister's murder investigation.
The bloodied bodies of Suzanne Armstrong, 28, and housemate Susan Bartlett, 27, were found in their home in Collingwood on January 13, 1977, after a neighbour heard the cries of Ms Armstrong's 16-month-old son, Gregory
Ms Armstrong had been raped and stabbed 29 times and left her on the floor in her bedroom.
Ms Bartlett, who police believe was either trying to save her housemate or raise the alarm, was caught by the offender and stabbed 55 times in the hall of the home on Easey Street.
Police believe they were killed on the night of January 10.
As she joined Victoria's homicide squad boss on Sunday to announce a $1 million reward for information on her sister's death, Gayle Armstrong expressed frustration about early errors.
"We weren't even interviewed," Gayle told reporters on Sunday.
"We had to make an appointment to go down to the police station to speak to police, which was really bad."
The sisters had planned to reunite in Hungerford, Queensland, where Gayle was working as a shearers' cook.
But Ms Armstrong stayed in Collingwood when she couldn't find anyone to look after baby Gregory.
Police have a DNA profile of the offender and 130 persons of interest, including 41 who have died since the murders.
But all eight prime suspects in the case were eliminated after DNA testing in 1999 and investigators working the case have no strong leads.
"I hate to say it but here's a million dollars," Gayle said.
"You can live the rest of your life in comfort - just say something."
Homicide Detective Inspector Mick Hughes said he didn't think someone could commit a crime with such brutality and go unnoticed.
"I don't say that he has told someone, but someone will know something about his behaviour or conduct that can point us to him," he told reporters.
He acknowledged mistakes were made in investigating the case decades ago but said it is now standard to interview the families of homicide victims.
"Even (despite) the mistakes those guys may have made in the early days, I know all they want is this investigation to be solved for the sake of both families."
