Another $1 million reward has been offered in a bid to track the people who murdered a Melbourne mother 30 years ago.

Maryanna Lanciana was 23 years old when she was shot dead at her Werribee home in July 1984.

Victoria Police believe her killers were also involved in the murders of underworld figures Demitrios Belias in 1999 and George Germanos in 2001.

Two $1 million rewards and indemnity from prosecution were recently offered for information about those murders.

Detective Inspector John Potter said there were people who knew the killers.

"We will put in place processes that protect anyone that comes forward," he said.

Police believe Dimitrios Belias (L) and George Germanos (R) were killed by the same person. ( Victoria Police: supplied )

Police said Ms Lanciana had a 23-month-old son who was asleep inside the house when she was killed.

Her husband had spent the night at his parents' house and found her body when he returned home on Tuesday afternoon, police said.

There were no signs of forced entry to the house.

Mr Belias was killed in an execution-style murder in a car park on St Kilda Road in 1999.

Mr Germanos was fatally shot in 2001 and his body was found in a park in Armadale.