An inquest into the 1975 execution-style killing of Shirley Finn has heard a cold case review in 2014 uncovered police corruption linked to the brothel madam's murder.

Ms Finn was shot four times in the head, her body found on a Monday morning in June, slumped over the wheel of her white Dodge Phoenix parked at the Royal Perth Golf Course.

She was killed just two days before a tax hearing where she had been threatening to blow the whistle on illicit dealings by high-profile politicians, businessmen and police.

Sergeant Brent Fletcher was the investigating officer in charge of the 2014 cold case review and subsequent investigation.

He told the Perth Coroner's Court that there had always been rumours of police corruption surrounding the case and, when asked what he discovered, said one case of corruption was found.

He said the officer in question had been referred to the police internal affairs unit, however no more details were given, including their identity.

Sergeant Fletcher said the initial review led his team to identify three main lines of inquiry that could lead to identifying Ms Finn's killer.

Phase one was to go back to all of the witnesses who claimed to have seen Ms Finn's car on Melville Parade the night before her body was found.

The next phase was to go over all calls made to Crime Stoppers regarding the case.

The third phase was looking into what came to be considered high priority suspects, which included former head of the Vice Squad Bernie Johnson, notorious Sydney underworld figure Arthur Stanley "Neddy" Smith and other lines of inquiry in NSW.

Sergeant Fletcher said between 1975 and 2014, 110 suspects had been identified.

When questioned he agreed none of the suspects had been definitively excluded and many had since died.

Ms Finn was rumoured to have had an affair with former WA Premier Ray O'Connor while he was Minister of Police. ( Facebook: Bridget Shewring )

He said of the many suspects, "there was certainly, I wouldn't say more weight, but more rumour and speculation, surrounding Johnson than some of the others".

Mr Johnson died in April this year and Smith is a convicted double-murderer, serving multiple life sentences in a Sydney jail.

When it became clear a coronial inquest into the murder would be taking place, Sergeant Fletcher said he "put the brakes" on the investigation.

He did interview Mr Johnson prior to his death but no details were revealed in court today.

Senior police figures not examined

Matthew Crowley, the lawyer representing Ms Finn's daughter Bridget Shewring, grilled Sergeant Fletcher on why some elements of the case had not been investigated.

In particular he was asked why witness accounts that named three police figures — former head of the Criminal Investigation Branch Don Hancock, former senior detective Arthur Simms and former officer James Boland — as the murderer had not been explored.

Former senior WA Police detective and CIB chief Don Hancock at died along with his friend Lawrence 'Lou' Lewis in a car-bombing in September 2001. ( ABC TV News )

Sergeant Fletcher said it was a matter of balancing resources and so if a person of interest had died, as in the case of Mr Hancock and Mr Simms, or if the evidence relating to those people were from hearsay, as with Mr Boland, they were not prioritised.

Mr Crowley also asked why forensic evidence, including fingerprints and hair samples from Ms Finn's car, had not been re-examined.

Sergeant Fletcher agreed that while physical evidence was critical, he believed it was a line of inquiry that was yet to be pursued.

The court also heard Sergeant Fletcher had been unable to find any evidence that the boot of Ms Finn's car had ever been opened.

Mr Crowley said this was concerning, especially considering previous evidence from Rose Black, Ms Finn's live-in girlfriend, that she had seen bags of money placed in the boot earlier on the night she was killed.

When asked whether forensic officers driving the car away without gloves or precautions was "ineptness or something more sinister", Sergeant Fletcher said it was a different time for forensics back then.

Ms Finn's white Dodge Phoenix has since disappeared.

Evidence was also revealed a map, drawn by a police sketch artist, of where Ms Finn's car had been found included a road that did not exist as shown.

The court also heard of an extensive report on Mr Johnson, written by former deputy police commissioner Les Ayton, who investigated police corruption between 1987 and 1992.

Sergeant Fletcher said he had been unable to confirm the document's existence and a request to the office of internal affairs to access the report had been denied.

As was later clarified in court, Sergeant Fletcher's responsibility while leading the review was to find evidence that would lead to the arrest of a suspect, not conduct a coronial investigation into the death.

Call for more witnesses

Since beginning in September last year, more than 50 witnesses have given evidence at the inquest.

Those who have testified ranged from former police officers, friends and family of Ms Finn to eyewitnesses connected to events over the weekend before her body was found.

Allegations of police corruption have long dogged the case, with many witnesses labelling Mr Johnson a key player in her murder.

Former WA Police detective Bernie Johnson was one of the officers who investigated Ms Finn's murder. ( Supplied )

Other names often mentioned include former WA premier Ray O'Connor — the police minister in 1975 who was allegedly having an affair with Ms Finn — and Mr Hancock.

This week the court again heard tales of Mr Johnson leading a group known as the "Purple Circle", described by former police officer Gary Timms as a collection of police officers and other influential people who had power above their rank.

On Thursday former officer Michael Regan said Mr Johnson led the purple circle.

"You don't 'f***' with Bernie," he told the court.

"When he said jump, you said 'how high?'."

Despite the many witnesses who have testified so far, the inquest appears no closer to determining who pulled the trigger.

On Friday the inquest was adjourned. It was revealed a number of inquiries were taking place, including a scientific investigation due to be handed down in September and further forensic investigations of the evidence.

Coroner Barry King made a plea to the public for anyone who has not already come forward with information on Ms Finn's murder to do so.

No date was set for the next hearings but Mr King said the inquest would likely resume in six months' time.