Deputy state coroner Barry King's findings were publicly released on Wednesday after a lengthy inquest into the 1975 killing wrapped up last year.

Ms Finn was shot four times in the head at point blank range.

The mother of three was found dressed in a ball gown, slumped in her car on the edge of Royal Perth Golf Club.

The inquest heard many allegations and rumours the assassination-style murder was arranged or executed by police top brass, with then-vice squad chief Bernie "The Bear" Johnson's name repeatedly popping up.

Mr Johnson died in 2018 and did not give evidence at the inquest as he had dementia.

"A great deal of the evidence implicated Mr Johnson, but the majority of it was so weak that, even taken as a whole, the evidence could not support a finding against him to the standard of proof required for such a serious allegation," Mr King said in his findings.

"In addition, evidence implicating other suspects could not be discounted entirely, which meant that it was not open to exclude the possibility that one of them was responsible."

Mr King said it was "disappointing and frustrating" that he hadn't been able to determine who killed Ms Finn.

But he noted that the investigation into her death was back in the hands of WA Police to follow up any further evidence that came to light.

The coroner identified 11 possible suspects including Johnson, former detective and convicted killer Roger Rogerson, Sydney hitman Arthur "Neddy" Smith and former WA premier Ray O'Connor, who was police minister in 1975.

Evidence was given that Mr O'Connor had an affair with Ms Finn.

"Mr O'Connor was clearly a colourful character," Mr King said.

"There is evidence indicating that he may have been involved with Ms Finn, and weak circumstantial evidence suggesting that he may have procured Ms Finn's death.

"However, none of that evidence comes close to establishing his involvement to the applicable standard of proof."

The inquest heard evidence Ms Finn had been paying police to avoid being raided and had threatened to name names unless she was helped with a substantial tax bill.

Several aspects of the initial investigation, even by 1970s standards, were "so incompetent" that the evidence obtained at the time was unreliable, Mr King found.

He said while there was a considerable amount of evidence implicating police in corruption related to prostitution, he could not exclude other potential motives for Ms Finn's killing.

Australian Associated Press