Two women, Suzanne Armstrong and Susan Bartlett, were found dead in their Melbourne house on Easey Street, Collingwood, in 1977. A man has been detained in Italy in connection with their murders.

On Thursday night, Australian eastern time, a 65-year-old man who holds dual citizenship with Greece and Australia was taken into custody at a Rome airport.

Victoria police will seek an extradition order for his repatriation to Melbourne.

In January 1977, Armstrong and Bartlett, together with Armstrong's 16-month-old toddler, were murdered in their leased terrace house in Collingwood.

The women’s bodies were found in the house on 13 January, three days after they had last been seen alive, with the child distressed and dehydrated but otherwise unhurt.

According to authorities, Armstrong, 27, and Susan, 28, had both suffered several stab wounds.

Unsolved for decades, the Easey Street killings, as they came to be called, were one of Melbourne's most well-known cold cases.

A $1 million prize was put out in 2017 for anyone with fresh information that could result in the apprehending and conviction of those who should be held accountable.

There have been several books and podcasts about the case.

While the investigation is ongoing, the chief commissioner, Shane Patton, said in a statement on Saturday that the arrest of the man was “an important breakthrough”.

“For over 47 years, detectives from the homicide qquad have worked tirelessly to determine who was responsible for the deaths of Suzanne Armstrong and Susan Bartlett,” Patton said.

“An enormous amount of work has been done by many, many people to bring us to the position we are in today … This was a crime that struck at the heart of our community – two women in their own home, where they should have felt their safest.”

Patton also recognised “the enduring resilience of both the Armstrong and Bartlett families, who have grieved for over four decades and no doubt this will be a very emotional time for them”.

The families of Armstrong and Bartlett requested privacy in a joint statement on Saturday afternoon.

“For two quiet families from country Victoria it has always been impossible to comprehend the needless and violent manner in which Suzanne and Susan died. The gravity of the circumstances surrounding their deaths changed our lives irrevocably,” the statement said.

“We will be forever grateful for the support and understanding shown to us by our friends and family over the past 47 years. It is difficult to sufficiently express our appreciation to Victoria police and the many investigators who have tirelessly pursued answers and justice for us over such a long period of time.

“The perseverance and dedication required to achieve the result today is something to truly behold. For always giving us hope and never giving up, we simply say, thank you.”