Police are defending their use of a breath-testing checkpoint to target euthanasia supporters as part of Operation Painter.
They said yesterday that the checkpoint was set up earlier this month specifically to identify people leaving an Exit International pro-euthanasia meeting in Lower Hutt.
The police have since referred themselves to their own watchdog, the Independent Police Conduct Authority.
The authority has received three other complaints - including from someone who was stopped by officers at the checkpoint.
Acting Wellington District Commander Inspector Paul Basham told reporters this afternoon that police were investigating a number of suspected assisted suicides.
They were looking into a death in June in which a particular Class C controlled drug was a contributing factor, he said.
There was no indication at the time that the death was suspicious, and the deceased was not suffering a terminal illness.
Mr Basham said the coroner referred the death to police, who started an investigation.
That investigation was still in its early stages but had revealed other deaths that required further investigation.
Police became aware of the Lower Hutt meeting as a result of their inquiries, and were worried about the welfare of those attending the meeting.
The checkpoint was set up in the interests of preserving life, he said.
"We believe our officers acted in good faith and what they did was reasonable."
Seven cars were stopped at the checkpoint and details were obtained from 10 people, he said.
Police subsequently visited nine people and offered them support.
"The information obtained during this checkpoint enabled police to take advice, and then provide support and information to those people who we had reason to believe may be contemplating suicide."
He said the preservation of life was central to the role of police and their intentions in this case.
Privacy Commissioner considering separate investigation
Privacy Commissioner John Edwards told Checkpoint with John Campbell he was troubled by the use of the checkpoint, and was seriously considering a separate investigation into the incident.
Mr Edwards said police collected information from people they stopped at the checkpoint, and had misrepresented why they were doing that.
He said that appeared to be a breach of the Privacy Act and there could be remedies for those affected.
Mr Edwards could not say if the police behaviour was illegal.