$1 million offered for 'missing piece' in double murder

A coroner determined in 2003 they were murdered by an unknown person but no arrests or charges have ever been laid.

But a 2025 forensic review has given the investigation a second wind that could lead to a resolution, with a little help from the public.

"We are almost there," Homicide Squad commander Joe Doueihi told reporters on Monday.

"I strongly believe - with the assistance of the community, the assistance of friends and associates of both Susan and Joanne - that this matter truly is solvable.

"We just need that little bit of information that puts this whole jigsaw puzzle together."

Police increased the reward for information from $100,000 to $1 million as they laid out their leads.

The women were last seen alive on May 11 before their bodies were discovered a week later. 

Investigations at the time led police to believe the killings were drug-related after they learned illicit substances were being sold from Ms Teterin's home.

On the morning of May 11, a call was made from a payphone about 200 metres from the Carrington residence.

Ms Teterin's system forced any interested buyers to call her home before attending to ensure there were no surprises at the door.

Officers don't know who made the call on that morning, but they believe the person responsible could help the investigation.

Ms Kay, on the other hand, had spent the morning shopping for groceries before heading to Ms Teterin's home.

"We can draw a strong inference that the person that made the phone call had contacted the residents to purchase drugs and then ... attended that location," Det Supt Doueihi said.

"There's a possibility that something has gone wrong, which may have resulted in the death of both women."

Ms Kay's sister Desiree urged anyone with relevant information to come forward as she paid tribute to her loved one.

"As a child, if there was mischief to be gotten into, she would find it," she said.

"(She was) fiercely protective of the people that she loved with a very loyal, strong sense of family - not perfect by any stretch but none of us are.

"Susan would be very annoyed if whoever it is gets away with it."