A man has been arrested in Italy over the 1977 murders of two women, Suzanne Armstrong and Susan Bartlett, who were found dead in their Melbourne home on Easey Street, Collingwood.

A 65-year-old man, a Greek-Australian dual citizen, was arrested at a Rome airport on Thursday evening, Australian eastern time.

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

Armstrong and Bartlett were killed in January 1977 in their rented Collingwood terrace house while Armstrong’s 16-month-old toddler slept in another room.

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.

Both Armstrong, 27, and Susan, 28, had been stabbed multiple times, police said.

The Easey Street murders, as they became known, was one of Melbourne’s most high-profile cold cases, remaining unsolved for decades.

In 2017, a $1m reward was offered for anyone who had new information that might lead to the arrest and conviction of people responsible.

The case was the subject of a number of books and podcasts.

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.”