Doris McCartney and Ronald Swann were found dead in their Keith Street home in Moorabbin on October 22, 1989.
Homicide Squad detectives arrested a 58-year-old man in Rowville, in the city’s outer south-east, this morning after a $1 million reward for information on the siblings’ murders was released last week.
Exclusive 9News images captured the man covering half of his face with a baseball cap as he sat in the back of a detective car while being driven to police headquarters.
“The Rowville man is currently in police custody being interviewed by detectives,” a Victoria Police statement read.
“A further update will be provided when appropriate to do so.”
A friend of Ms McCartney discovered the bodies at the time and contacted police.
Ms McCartney, 71, and Mr Swann, 69, appeared to have been assaulted.
The man’s arrest follows an “extensive and exhaustive investigation” over the past 31 years.
Detective Inspector Tim Day last month said investigators were determined to solve the case and provide answers to the family.
“This is a family that has suffered the loss of two loved ones in the most horrific circumstances, without ever knowing why,” he said.
“Over the years we have followed up a number of avenues of enquiry and interviewed several people.”
Further lines of enquiry had only emerged recently, Det. Insp. Day said.
Ms McCartney was a widower and her younger brother, a World War II veteran, had moved into her Keith Street home to support her.
Police have previously said there was no sign of forced entry into the pair’s home and nothing had appeared to be taken.
“From all accounts, they lived a quiet life,” Det. Insp. Day said.
A number of people had previously been interviewed about the murders, but no one has ever been charged.
Devastated son Ian McCartney last month said he thought about the deaths of his beloved mother and uncle every day.
“There’s not a day in 31 years that I haven’t thought about it,” he said.
“Sometimes it’s hours, other times it might be five minutes.”
The man remains in police custody and is yet to be charged.