UPDATED: 6.24PM The Mental Health Foundation is moving to reassure the public in the wake of what it's calling a horrific tragedy.

LISTEN ABOVE: Larry Williams speaks to Labour's police spokesperson Stuart Nash about his issues and concerns of the handling of Bremners case. 

Mr Nash said it doesn't make any sense. 

"Something's not right when the police have told the public don't worry, the man poses no threat, when obviously he did. I just want to know where the police got that information from."

Ross Bremner was found dead alongside the bodies of an elderly couple, days after allegedly killing his mother and critically injuring his father in a knife attack.

Foundation boss Shaun Robinson said while Mr Bremner had serious issues with mental illness, the vast majority of people who experience mental illness are perfectly safe and not violent towards others.

"These are isolated cases, and there may be many other factors that have contributed to the tragedy in addition to Mr Bremner's mental illness."

Shaun Robinson said half our adult population experience a diagnosed mental illness of some point.

DHB spokesperson Lydia Ayson said Bremner had been a client of Mental Health and Addiction Services for 13 years.

"He had a number of brief inpatient stays at 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 2013, Ross Bremner had been living in the community under the care of his GP and with DHB support.

The DHB will be reviewing its involvement in his care.

"We'll 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."

Mental Health Foundation CEO Shaun Robinson said it's too early to say what might have been done differently, in terms of services and support, to prevent this.

"We would be supportive of the DHB taking that action, and hopefully being committed to making whatever improvements they can that are identified in that review."