Perry Kouroumblis had been a student at the school one of the victims worked at and lived a short walk from where they were brutally killed.
The murders have gone unsolved for 47 years.
But 65-year-old Perry Kouroumblis was detained at an Italian airport after flying in from Greece.
Police will allege he stabbed Suzanne Armstrong and Susan Bartlett to death at their Collingwood home in 1977, leaving Armstrong’s 16-month-old son unharmed.
His brother Tony spoke for the first time today.
He said he was “just numb” and ” just shocked”.
“I definitely don’t think he’s capable of doing anything like that,” Tony said.
At the time of the deaths the brothers lived together on Bendigo Street just a 350-metre walk from 147 Easey Street.
The then 17-year-old was a student at Collingwood High School, where Bartlett worked as an arts and crafts teacher.
Retired homicide detective Ron Iddles said he pulled the suspect over a week after the vicious crime.
“I searched the car and found a knife in the boot. I saw what I thought were blood stains near the handle,” he said.
Iddles handed the knife to detectives.
In 2017 police reopened the case.
Tony and other relatives provided detectives with a DNA sample.
Perry said he’d do the same but instead flew to Athens.
“If he was gonna hide too, he wouldn’t have stayed here for 40 years plus after that,” his brother said.
The homicide squad has 45 days to present a brief of evidence to an Italian court which will decided whether or not to extradite him back to Australia.