Kath Bergamin, 37, disappeared from her Wangaratta home in August 2002, with a coroner later concluding she was murdered, but her body has not been found.

On Thursday, Victoria Police revealed five people had been interviewed across the past week over Ms Bergamin's disappearance.

They included a 60-year-old Cheshunt man, a 51-year-old Wangaratta man, a 37-year-old Melbourne man, a 33-year-old Docker woman and a 30-year-old Yoogali man.

All were released without charge.

The mother-of-three disappeared on August 18, 2002, from the home she shared with a friend, months after splitting from her husband John Bergamin.

Mr Bergamin and the couple's eldest son, Stephen Bergamin, were previously suspects in the case.

A coroner in 2008 said there was not enough evidence to establish who killed Ms Bergamin.

A number of exhibits have also undergone further DNA testing and forensic re-examination.

An anonymous letter with specific information about the murder, including who was involved, was received by police in March 2017.

They are still keen to hear from the mystery letter-writer, reminding the public there is a $1 million reward for information that leads to the conviction of Ms Bergamin's killer.

The author may also be granted indemnification from prosecution by Victoria's Director of Public Prosecutions if the information identifies the principal offender or offenders, Victoria Police say.

Australian Associated Press