Two psychiatrists later diagnosed Ahlquist with paranoid schizophrenia and he was found not guilty of murder on the grounds of insanity.
Graeme Moyle has written to Prime Minister John Key and Cabinet ministers demanding more accountability for health professionals whose failures lead to serious events such as homicides.
He said such failures included dismissing information about patients from their family and friends, refusing patients admission or misdiagnosing them.
Other recommendations included immediately admitting patients posing a risk to themselves or others to dedicated units and treating such presentations as "psychiatric emergencies"; regarding friends and families' information about patients as "crucial" when diagnosing them; and boosting medium- to long-term bed numbers in psychiatric hospitals.
Mr Moyle also wants families of victims killed by mental health patients to be informed of their release rather than receiving "one-off" statements that they may be released.
"Colin's death should never have happened - it was completely preventable," he told the Herald.
"We are just lay-people, but if I was in that environment and someone came up to me and said they are going to kill somebody, I'd shut the door and lock it for a while."
The Auckland DHB has apologised to Mr Moyle and invited him to a sit-down, but he says he is not prepared to accept anything less than the Government making his suggested changes.
"I don't like losing, so I'm probably in for the long haul here," he said.
Questions by the Herald were referred to the Ministry of Health when the newspaper asked whether Mr Moyle's recommendations would be considered or were already in place.
Ministry acting director of mental health Dr Susanna Every-Palmer said in a statement that a number of internal and external inquiries were undertaken following Colin Moyle's death.
"Services have carefully considered and implemented the recommendations that have resulted from those inquiries."
Auckland's acting director of mental health, Dr Debbie Antcliff, said the DHB had taken "immediate action" to implement recommendations made by the Health and Disability Commissioner that related to events leading up to Mr Moyle's death.
The board commissioned the new independent review on the commissioner's recommendation.
Dr Antcliff said it found there had been a "profound change in culture and clinical standards" since 2007-08.
"We have come a long way over the last three years and now have the systems and processes in place that would ensure a patient in a similar situation to Mr Ahlquist would receive appropriate care."
