Police police believe the blaze was deliberately lit, but have never found out who was responsible.

On Monday, arson squad detectives appealed to the public for clues about what started the fatal Ferny Creek bushfires in January 1997 – and have added an incentive.

There is now a $1 million reward for any information about the fire, which killed three people, destroyed 42 homes and damaged 45 more.

On 21 January, about 12.30pm, husband and wife, Graeme, 26 and Jennifer Lindroth, 24, were at their Seabreeze Avenue home in Ferny Creek with their 50-year-old neighbour Genevieve Erin when the house was destroyed by fire.

All three were found dead in the garage.

Despite extensive investigations and a reward on offer, police have been unable to locate the person or persons responsible and no charges have been laid.

Inspector Michael Roberts of the arson and explosives squad said he believed that the arsonist chose that day for it's dry, hot conditions with an intent to cause extensive damage.

"By making a renewed appeal to the public and finding the person responsible for such senseless devastation, we are hoping to provide the families of the victims with some answers." he said.

A reward of up to $1 million will be paid at the discretion of the Chief Commissioner of Police, for information leading to the apprehension and subsequent conviction of the person or persons responsible for the suspicious fires.

The Director of Public Prosecutions will consider the granting of indemnification from prosecution to any person who provides information as to the identity of the principal offender or offenders in this matter.

Anyone with fresh information should contact Crime Stoppers on 1800 333 000.