Katie Tangey, 27, died along with her family's dog after arsonists hit the wrong address while she was minding the home in Truganina in Melbourne's west, in the early hours of January 16.
Shortly after 2am, two people were captured on CCTV getting out of a dark-coloured vehicle - similar to a BMW X3 or X5 – outside the address.
There's an explosion and the pair leave the area.
Ms Tangey was inside the three-storey property, which belonged to her brother and his wife.
Anonymous calls to Crime Stoppers provided police with some information, including one in which the caller gave a name believed to be a pseudonym or nickname.
Investigators want that caller to make contact and provide them with more information.
Detective Inspector Chris Murray said police are close to solving the crime.
"Those responsible for Katie's death know they targeted the wrong house and they have to live with the knowledge that they are responsible for the horrific death of a completely innocent young woman," Det Insp Murray said.
"We believe we know who directed this crime, and we know we are getting closer to proving who was responsible for carrying it out on the night."
He called on anyone with information to come forward.
"Five hundred thousand dollars is a lot of money – hopefully it will encourage those people out there who do know something to do the right thing and come forward. Katie's family deserve answers," he said.
Detectives confirmed in February that Victoria Police believe the arson attack was likely linked to the illicit tobacco dispute in Melbourne.
More than 100 tobacco shops and other businesses have been firebombed in the conflict over multimillion-dollar profits, which has also involved attempts to extort individual store owners.
Investigators believe the arson that claimed Ms Tangey's life had the hallmarks of a targeted attack but hit the wrong address.
She had nothing to do with the illicit tobacco trade, police have confirmed.
Police previously executed a search warrant at a Dandenong home in June, when they seized a number of mobile phones which are being forensically examined.
In April, police released a computer-generated image of a man they believe may have been involved in the incident.
He is described as 25 - 30, with a slim build and of Middle Eastern appearance.
The reward will be paid at the discretion of the chief commissioner of police for information leading to the apprehension and conviction of the person or persons responsible for the death of Ms Tangey.
The director of public prosecutions will also consider granting indemnification from prosecution to any person who provides information.
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