The Waikato DHB is reviewing its mental health care processes after Ross Bremner's murderous rampage last week.
Bremner killed his mother, Clare, and left his father, Keith, fighting for his life in their Otorohanga home last Tuesday.
His own body was found alongside those of elderly Te Kuiti couple Mona Tuwhangai and Maurice O'Donnell four days later, on Friday.
Police are still piecing together what happened as the two families begin to come to terms with the tragedies.
Bremner was believed to suffer from schizophrenia, which may have been drug-induced.
He had been under the care of the Waikato DHB.
DHB spokeswoman Lydia Aydon said an independent review will be carried out following the terrible events.
"Our thoughts are with the family and community at this difficult time," she said.
"Waikato DHB can confirm that Ross Bremner was a client of our Mental Health and Addiction Services and had been since 2003."
She said he had a number of brief inpatient stays in Henry Bennett Centre at Waikato Hospital from October 2003 to January 2007.
He had no further admissions until April 2013 when he spent six weeks in hospital. Since May 2013 he has been living in the community under the care of his GP and with the support of the "relevant DHB services".
"As with any serious incident of this nature, and in compliance with nationally agreed best practice, we will be conducting a review of our involvement in this client's care.
"We will be engaging an independent psychiatrist to head the review and, as part of the review, we will talk to other providers who helped to support Ross in the community. The review is expected to take a number of weeks."
Bremner is the third Henry Bennett Centre patient to die in controversial circumstances in recent times.
A 24-year-old woman was found dead near the Waikato River while on leave from the centre in July.
Her death came nearly three months after the Ministry of Health published what the Green Party called a "damning" report on the DHB's mental health services.
Questions have been raised about Waikato's mental health services since the death of Nicky Stevens in March last year.
Aged 21, Stevens was found dead in the Waikato River, after being released from the centre.
Meanwhile Donna Tuwhangai told Radio New Zealand she had only seen Tuwhangai and O'Donnell last Sunday when they buried her son's placenta on the family's Kinohaku property.
She believed she was one of the last people to see the couple before they are understood to have been killed by Ross Bremner.
She ate lunch with her aunty Mona Tuwhangai and uncle Maurice O'Donnell after the placenta was buried on the family land beside many others, RNZ reported.
"It was a lovely sunny day on Sunday, and I'm glad I got to spend the day with them."
She described the couple as kind and welcoming. "Aunty and uncle were well known for their Manaaki Tangata (hospitality) and their door was never locked. Knowing their nature, it's a possibility that could be a reason that this has occurred," she told RNZ.