Letters and drawings from a dead friend were among items seized by police as they conducted anti-euthanasia searches.

As more speak out about the police operation – linked to a police checkpoint targeting Exit International meeting attendees – the scale of police searches on mostly-elderly Wellington women is becoming clear.

While different people were targeted in the searches to those stopped at the checkpoint, they all fell under the umbrella of a police operation, code-named "Painter".

The legality of the police checkpoint is now being investigated by the Independent Police Conduct Authority after multiple complaints.

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Exit International director Philip Nitschke has supplied letters, sent to him by Wellington members, detailing searches during Operation Painter.

One woman described how she got a call from police "saying they were at my house with a search warrant and would I return home as they wanted to speak with me".

She could not get home till later but police searched her property, found a spare key and spent two-and-a-half hours searching her home, she said.

Police seized her laptop and another "belonging to a club I belong to", a computer tablet, USB sticks, two digital cameras, documentation relating to her mother's death, funeral and will, as well as books and documents related to voluntary euthanasia.

"They also took a couple of letters written to me by [an] Exit friend, prior to her death – warm, friendly communications filled with little drawings which she loved to do."

Wellington City Area Commander Chris Bensemann said police carried out six searches on October 7 "in relation to the ongoing investigation into the serious criminal offence of aiding and abetting suicide", leading to one person being charged.

"A number of items seized have been returned to their owners, and police are working through the process of returning the other items once we have completed the necessary steps to do this. We are very mindful of the need to do this as quickly as we can."

Another Wellington woman – who had her supply of class C euthanasia drug Nembutal seized in a three-hour search – also had her computer and tablet taken.

This meant she was unable to Skype her United-Kingdom-based, wheel chair-bound sister, who had severe dementia.

"I am devastated to say the least as it was such a feeling of violation then, and especially after they gave me the list of what they had taken and I realised just how thoroughly they had searched absolutely everything in my house."

Nitschke said on Monday that none of the items had been returned to the two women and neither had been charged.

Elisabeth Meylan, who got stopped at the checkpoint, which was followed by a visit from police, said she got a second visit from police late last week – after police had referred themselves to the IPCA – from some "very, very nice police women".

They were there to reassure her the operation was carried out with the "best intentions", she said.

The IPCA has confirmed it is officially investigating the police checkpoint. It received four complaints or referrals about it, including the one from police.

Police have been approached for comment on why they did not give the option of a support person and why they seized such wide-ranging items during the searches.