There have been no reported sightings of a man who vanished after the stabbing of his parents at their home in Otorohanga on Tuesday night, police say.
Claire Bremner was found dead and her husband Keith remains under police guard in an induced coma after major surgery.
A manhunt for the couple's 34-year-old son, Ross Douglas Bremner, was launched following the attack.
Members of the public were urged to alert the police if they saw Mr Bremner, or a 2003 Holden Vectra with the registration number BGP561.
Detective Senior Sergeant Ross Patterson said neither Mr Bremner nor his car had been seen since the attack.
"Ross, if you're listening to the media and you hear this, I ask you to contact me ... and we can just talk about this, or just come to the police so that we can resolve the issue and move forward.
"We just want you to come, come in and be unharmed."
Mr Patterson said 16 staff were working on the homicide investigation, but they had not heard of any sightings of Mr Bremner in the area or elsewhere.
He said a post-mortem had been performed on Mrs Bremner's body yesterday, and the crime scene was being examined.
Waikato acting district commander Ngila Hassan said the public were coming forward with possible sightings of him but none had been confirmed.
She said there was a possibility Mr Bremner may try to visit his father in hospital.
Around 20 police were on the ground in Otorohanga, where the search remained focused, she said..
A Waikato District Health Board spokesperson said on Wednesday that Mr Bremner had been a mental health patient, and was last in in-patient care in 2013.