A dig in Kawerau by police investigating the 1970s disappearance of Mona Blades has failed to find any key evidence.
Ms Blades' disappearance on May 31, 1975 while hitchhiking from Hamilton to Hastings has remained unsolved but information police received late last year led them to the property in the Eastern Bay of Plenty town.
Bay of Plenty field crime manager Detective Inspector Mark Loper says the information led to sonar work at the property, and that work led to the excavation.
"Today's operation has involved excavating to a depth of approximately 80 centimetres, followed by probing with rods a further 80 centimetres," he said on Thursday.
"This work has not uncovered any item of interest and police and workers will shortly leave the property."
The investigation on Thursday was done with the permission of new owners who bought the property last year.
"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," Det Insp Loper said.
"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."
Ms Blades was last seen sitting in the back seat of an orange Datsun station wagon on Cambridge Rd, Hamilton.
A woman fitting her description was spotted in the back of a car on a dirt road off the Napier-Taupo highway later that day but the car was empty when seen soon afterwards.
When police said two weeks later that they were looking for an orange Datsun, John Freeman, who hired an orange Datsun that weekend, killed himself after shooting and injured a student at St Cuthbert's College in Auckland.