VICTORIAN arson squad detectives are calling on Daylesford-district residents to help solve a 20-year-old suspicious death in Yandoit.

Arson squad detectives have reopened the investigation into the death of Sandra White, 34, who was found in a burnt-out caravan beside her small stone cottage.

She was believed to have been cleaning the caravan where her son, Timothy, lived when the fire broke out on Sunday, August 12, 1985.

The fire is believed to have been deliberately lit because the caravan wasn't connected to gas or electricity.

Arson Squad Detective Inspector, George Cooney, said police had a strong suspicion about who was responsible.

He said police were seeking a man, 54, who had a close relationship with Ms White at the time.

He has proven hard to keep track of since 1986.

The man was a metalworker who worked in Melbourne and police believe he has been moving back and forth between Australia and England.

Det Insp Cooney said there may be people who had lived in the area who were not spoken to by police and may have vital information that could assist them.

"Someone may have information," he said.

"They may think it's of no value, but it may be valuable to police."

Det Insp Cooney said Ms White and her son had a "real matey" relationship and he suffered as a result of his mother's death.

"Tim wants to fill in the gap and put the puzzle together," he said.

He said the death also put a lot of strain on Ms White's parents.

"If we get that right bit of information, we will have enough concrete evidence to find the person we are looking for," Det Insp Cooney said.

A coronial inquest in December 1986 in Castlemaine could not establish the cause of death or the circumstances leading to it.

People who may think they have information about the man's movements in 1985 or know anything since are asked to call Crime Stoppers on 1800 333 000.

Callers can remain anonymous.