WA Opposition Leader Mark McGowan says police have shown poor judgment after detectives seized documents from The West Australian newspaper as part of an investigation of pro-euthanasia doctor Alida Lancee.
The newspaper said it had co-operated with two major crime squad detectives and handed over all interview notes, emails and audio and visual recordings related to Dr Lancee.
The GP said in media interviews last month that she had given a lethal injection five years ago to an 80-year-old woman who was dying of emphysema, prompting police to raid her clinic as part of a homicide investigation.
Mr McGowan, who supports legalising voluntary euthanasia, questioned whether it was in the public interest for police to pursue Dr Lancee instead of "thousands" of other crimes.
"I think the police need to pull back and exercise some judgment as they do every day of the week in relation to a whole range of offences," the Labor leader told reporters.
"The police only have so many resources and I think they need to worry about things that matter most to people: armed robberies on our streets, dangerous drivers in our community and the methamphetamine crisis."
Mr McGowan said it was time for voluntary euthanasia or assisted suicide laws to be brought before the WA parliament and debated since he believed most people supported it.
South Australia has just introduced voluntary euthanasia legislation, which will be subject to a conscience vote by all MPs, while the Victorian Labor government is also poised to introduce similar laws.
A social media campaign in support of the new laws has been launched featuring cancer sufferer Kylie Monaghan, whose disease has spread to her liver and bones.
WA police would not comment, although Commissioner Karl O'Callaghan said last month he instructed officers to investigate Dr Lancee without fear or favour.
She is not currently commenting but has previously said there should be a legal means to shorten the dying process for people where "suffering remains unbearable during the terminal phase of their illness".
Thursday marked the 20th anniversary that carpenter Bob Dent, a prostate cancer sufferer, became the first person to lawfully end their life during the nine months that the Northern Territory was the world's first jurisdiction to legalise euthanasia.
The NT's chief minister at the time, Marshall Perron, said on Friday there was greater support for legal euthanasia than ever - about 80 per cent in WA - given medical advances meant "decaying bodies" were kept alive longer and died more slowly.
Mr Perron criticised WA Health Minister John Day, who recently said the legal status of euthanasia was too complicated for a legal fix, pointing out the practice and assisted suicide were legal in many parts of the world.
