Police excavation of a property in Kawerau today has not revealed any new evidence in their investigation into the 1975 disappearance of Mona Blades.

Mona disappeared in 1975 on May 31 when she was hitchhiking from Hamilton to Hastings.

Police attention in the Mona Blades cold case is focused on Kawerau. Image: Google Earth.

Police were unable to solve the case, but it remained open and today it was re-examined owing to the receipt of new information given to them last year.

Detective Inspector Mark Loper says while it is not possible to discuss the nature of the information, he says it prompted sonar work to be undertaken at the property.

This led to the excavation.

'Today's operation has involved excavating to a depth of approximately 80cm, followed by probing with rods a further 80cm,” says Mark.

'This work has not uncovered any item of interest and police and workers will shortly leave the property.”

Mark says the property under investigation in Kawerau was purchased by its present owners last year. Permission was granted by them for police to undertake today's work.

Mark says an unsolved murder case is never closed and that police continue to do their best for victims of crime, regardless of the age of the case.

He says unsolved cases are periodically reviewed to ascertain whether any new information has developed, or if law or technology has changed that may shed new light on the case.

'Files like this always remain open waiting for new information or a situation to change, and we regularly review ‘cold cases' in a renewed effort to try and solve them.

'The recent arrest of a Rotorua man in connection with the 32-year-old murder of Rodney Tahu in Turangi is another example of that.”

Mark encourages anyone with information about any historic homicide to come forward to police.

'Relationships and allegiances change over time, and sometimes people just want to get things off their chest.

'If you have any information about any homicide, especially information not previously disclosed to police, please come forward with what you know.”

Mark says information can also be provided anonymously via the independent Crimestoppers line on 0800 555 111.