Philip Nitschke, director of Exit International, confirmed to the Herald this afternoon that Treadwell's death is believed to have sparked the controversial police investigation which saw police set up a fake drink-drive checkpoint targeting attendees of an Exit International meeting in Lower Hutt earlier this month.
"She was a member of Exit for a number of years, and we understand that she was able to end her life," Nitschke said.
"I understand that that's formed the basis of the original inquiry by the coroner into the use of the drug Nembutal and for people taking this step."
It was believed that this inquiry sparked the police investigation which led to the fake checkpoint, he said.
Dr Philip Nitschke, director of Exit International. Photo / file
Nembutal was a drug which many people intent on euthanasia "try to get hold of", Nitschke said, as "it's considered the best and most peaceful drug to be able to use to end your life".
"Many of our members set out to get that drug and quite a few succeed," he said.
Importing it is a crime, as it's classified as a Class C controlled drug in New Zealand.
This morning the Wellington chairwoman of the Voluntary Euthanasia Society, Susan Dale Austen, known as Suzy, appeared in the Wellington District Court, charged with importing pentobarbitone.
The 65-year-old Lower Hutt teacher did not enter a plea.
Austen confirmed to the Herald she was the chairwoman of the Wellington branch of the Voluntary Euthanasia Society, but declined to comment further on the charges.
She also declined to comment on whether the charges were related to a false police drink-drive checkpoint set up to target attendees of an Exit International meeting in Hutt Valley earlier this month.
Yesterday, Wellington Acting District Commander Paul Basham said the fake checkpoint was established as part of an investigation into a suspected assisted suicide in June.
He also confirmed that further deaths are being investigated as part of Operation Painter.
A police spokeswoman confirmed to the Herald this afternoon that the charges arose from the Operation Painter investigation. They were not connected to the checkpoint, she said.
"Susan Dale Austen appeared in Wellington District Court today on two charges of importing the class C drug pentobarbitone," she said.
"The charges arose from the ongoing investigation which we announced yesterday, not the checkpoint operation."
Exit International was "anxious of course" about Austen, Nitschke said.
"We're worried about ... Suzy, a long term leader of Exit in the Wellington area, she's a much loved person in the organisation.
"Not for them the worry whether mum has 'fallen down the stairs' at home or worrying phonecalls from her neighbours.
"No feelings of stress or guilt for the family members who scarcely have time for their meeting their own needs.
"Just peace of mind that mum is in the right place for the support she needs at this stage of her life. And peace of mind for me that I know I will not have to go on suffering for many more useless years."
Toxic to humans
According to the UK's department for Environment, Food and Rural Affairs (Defra), pentobarbitone is commonly used as a veterinary drug to put down animals. However, small doses can be lethal to humans.
It is described as a "potent hypnotic and sedative", which "is toxic if swallowed" and can be absorbed through the skin.
"This is a potent drug, which is toxic to man," a Defra information sheet on the drug says.
It adds that a dose as small as 2ml can have "serious CNS [central nervous system] effects" in human adults, and a dose of 5ml "has been reported to be fatal in humans".
The Ministry for Primary Industries (MPI) also recommends its use to euthanase animals.
