Despite his unusual appearance, it was the glint of blood on his face that drew attention.

Olsen had just finished a mammoth drinking session with friends at Kings Cross and Oxford St, where he was asked to leave gay clubs for being a nuisance.

By the early hours of August 22, 1992, Olsen found himself at Rushcutters Bay, a well-known gay beat in the eastern suburbs.

Uneasy on his feet, Olsen regained his balance as he stepped across the timber wharf, just metres from the icy harbour below.

A witness stopped him, after noticing his bloodied appearance, and asked if he was OK.

"I'm perfectly alright thank you," Olsen told the passer-by.

But less than an hour later the gay man's body was found floating in the water.

Paul Rath was on various medication for his nervous condition, but a walk up to North Head in Manly was often enough to calm him.

The 27-year-old would sit on the cliff top, dangling his legs over the edge as pounding waves smashed onto the rocks below.

An isolated pocket of North Head, near Fairy Bower, was a popular gay beat, but there was no evidence Rath was homosexual.

In 1997 his body was found on the rocks below his favourite sitting place.

When Samantha Raye's body was found at South Head in 1989 an empty vial of insulin, a syringe and a packet of valium tablets with empty blisters littered the rocks nearby.

The transsexual, who was diagnosed with diabetes, left a note at home: "At lighthouse: will be back?"

Sydney's dark shadow

Looked at individually, these deaths appear to be due to drowning, misadventure or suicide.

Yet they are now among a list of cases long touted as belonging to the spate of gay-hate crimes that cast a dark shadow over Sydney between the 1970s and late '90s.

Whether there was a gay-hate motive involved is a question a NSW Police taskforce is seeking to answer with a review of into 88 deaths dating to the 1970s.

A team of eight detectives attached to Operation Parrabell are meticulously reviewing every archived document in these cases in a bid to decide whether gay hatred motivated the victim's death.

"The true beauty of Parrabell is it is an open and honest and transparent investigation and we are here to make sure that happens," Superintendent Tony Crandell told Fairfax Media.

"Whether the outcomes are good or bad for the police I am not concerned about that.

"We will report the truth."

About 30 deaths previously identified as unsolved - ranging from declared suicides to savage bashing murders - are included in the 88 cases.

They were highlighted in research by former NSW Police gay and liaison officer Sue Thompson and criminologist Stephen Tomsen.

Between them, the academics came up with the tally after reviewing media articles, court records and, in Ms Thompson's case, through interviews with investigators.

The research was guided by possible gay-hate indicators such as offender admissions, proximity to a known gay social venue or beat and the frenzied nature of attack.

There is concern in police circles that some cases devoid of homophobic sentiment have made the list. In some cases, the victim wasn't homosexual, may have committed suicide or died near a known gay beat.

Serial killer Mark Valera's victims - former Wollongong mayor Frank Arkell and David O'Hearn - were identified in the research, as was murdered paedophile Trevor Parkin.

Valera murdered O'Hearn at his Albion Park home in 1998 before cutting of his head and dismembering his body.

Two weeks later Valera, who fantasised about Satan, murdered Arkell as he was awaiting trial on paedophilia charges.

Convicted child sex offender Trevor John Parkin was bashed with a bowling pin and partially dismembered in after the 1997 killing.

A teenager was charged over the murder, with a court hearing Parkin made an unwanted sexual advance.

There has also been criticism levelled against the police for not identifying gay-hate crime cases in the past.

"There were a staggering amount of deaths and assaults involving gay men in public places from the 1980s to the early 2000s, and we believe that many of these murders were mischaracterised as suicides or misadventure," ACON chief executive officer Nicolas Parkhill said.

The NSW Coroner's Court is poised to hold a third inquest in July into the 1988 Manly cliff-death of Scott Johnson.

His family launched their own investigation into the 27-year-old's death after a coronial finding in 2005 that two gay men and potentially a third were murdered at the Bondi-Tamarama cliff tops in the 1980s.

Mr Johnson's family don't believe he committed suicide.

Among the other cases to be reviewed is the murder of 35-year-old Wayne Tonks, who was found bashed and tied up with a plastic bag over his head in his Artarmon unit.

There are also multiple "suicides" at Manly's North Head which research has raised questions about, including Rath.

The gay bashings that tarnish Sydney's past occurred at a time of fear and panic around HIV/AIDS and when "gay men were easy targets with not many allies".

"The violence that was committed against our community has never been fully acknowledged and the trauma of this remains unresolved," Parkhill says.

"At the time there was little effort to prevent this wave of crime confronting our community, and there has been a subsequent lack of resources given to delivering justice for these men."

The Unsolved Homicide Team has previously reviewed a list of 30 cases referred to by researchers as unsolved and agreed that eight are possible or probable gay hate murders.

Fairfax Media understands the remaining cases cannot be determined because of other likely motives, including robbery.

It is understood in at least one case - based on anecdotal information given to researches - detectives haven't been able to find a death certificate or coronial file.

The Surry Hills review will use 10 bias-indicators from the FBI over the next few months to assess whether the 88 cases are gay hate crimes.

The process will focus on the motive of an offender and whether he or she is driven by a hatred for homosexuality rather than robbery or other reasons.

Any fresh information will be sent to the unsolved homicide team for investigation.

Superintendent Crandell, the police force's LGBTI corporate sponsor, has also asked the detectives to tell him if the investigations were thorough.

"And the reason I ask them that is because, you talk about sore points in the community, that is a sore point," Superintendent Crandell says.

"Because if what they are saying is in fact correct, and the NSW Police Force and investigators were homophobic during that period of time, not only were they homophobic but they didn't do their jobs properly because that homophobia drove their performance as detectives.

"So I want to know whether or not that is the case."

Professor Tomsen, who identified 74 anti-homosexual killings between 1980 and 2000, was "uncertain" the police review would achieve its objective and questioned whether the FBI indicators were too narrow.

Asked whether the investigation could challenge his research findings, Professor Tomsen said: "I still know that I actually have a national and international reputation and my work has been...cited all around the world."

Investigators hope to have Operation Parrabell finished in the next few months.

The probable eight: Unsolved homicide's likely gay-hate crimes

The bashing of a band manager on a popular gay nightclub strip, a death wrongly deemed a fatal fall and a case where the alleged offender got away on a technicality.

Of 30 deaths dating back to the 70's and suggested as unsolved cases, NSW detectives have identified eight that are probable gay-hate crimes.

It is understood the remaining weren't determined because other motives could have been at play.

The Unsolved Homicide Team carried out a review of these 30 cases after research, reported in The Sydney Morning Herald in recent years, suggested they may be unsolved gay hate crimes.

Fairfax Media can reveal which eight cases the detectives agreed were probably gay-hate driven.

ACDC manager Crispin Dye was out with friends in Darlinghurst and Surry Hills on December 22, 1993, celebrating the release of his first CD release.

Near Taylor Square, just off Oxford St, he was set upon by three youths, bash and robbed in the early hours of the next morning.

His attackers got away with his wallet, suggesting that robbery was a motive.

However Mr Dye's homosexuality means gay-hate motivation can't be discounted either.

In 2014, a $100,000 reward was announced to find the killer.

Less is known about the death of William Allen, who was bashed to death at Alexandria Park - a popular gay beat - in 1988.

Detectives have reasoned that he too was probably the victim of a gay-hate assault.

Martial arts expert Raymond Keam met a similar fate in January 1987, when he was fatally assaulted in Alison Park at Randwick.

Cyril Olsen's death at Rushcutters Bay in 1992 was initially declared a drowning after an inquest. But police suspect the 64-year-old was the victim of a gay bashing before he fell in the water.

Police have also agreed that three high-profile deaths or disappearances from the Bondi-Tamarama cliff tops were probably gay hate crimes.

Thirty-one-year-old John Russell's body was found on the rocks below the scenic Bondi to Tamarama walk in November 1989.

The initial police investigation put his death down to "multiple injuries sustained...when he fell from a cliff".

Four months earlier, keys belonging to TV present Ross Warren were found on the rocks in the same area, but his body was never found.

In 1987, frenchman Gilles Mattaini, who enjoyed walks along the Bondi to Tamarama route, disappeared.

Years later reports surfaced about groups trawling the Marks Park area in the 80's looking for gay men to bash and throw off the cliffs.

Following a 2005 inquest, deputy state coroner Jacqueline Milledge found Mr Warren was murdered and Mr Russell was thrown off the cliff.

She also found Mr Mattaini likely met a similar fate.

Rewards totaling $300,000 are also in place for information leading to an arrest and conviction of the three men's deaths.

The eighth case identified as a gay hate crime is the bashing of Richard Slater in Newcastle on December 19, 1980.

The 69-year-old married man was found semi-concious at Birdwood Park, Newcastle.

Someone was convicted over his death after telling a friend he was going to the gay beat to find a homosexual man to assault and rob.

However, the charges were later dropped.