Warning: Graphic content.

The depraved writings by the Derek Percy fill 35 tea chests with terrible fantasies about the rape, torture and murder of children.

Somehow, while incarcerated for the mutilation and murder of a child, Derek Percy managed to secretly amass the files, clippings, and his perverted handwritten diaries in a Melbourne self-storage unit he rented from prison.

For 20 years, the material lay undiscovered until Victoria Police detectives were led to the vile cache and found it their unenviable job to sift through the documents and objects.

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Derek Percy, as he appeared in a police mugshot not long after his arrest. Photo / News Corp Australia
Derek Percy, as he appeared in a police mugshot not long after his arrest. Photo / News Corp Australia

To their horror, but unsurprisingly, some of the "torture fantasies" would prove real.

They were the shocking desires of one of the nation's worst sexual sadist going back decades.

Slowly, Victoria Police Senior Sergeant Detective Wayne Newman began to match the writings with some of Australia's unsolved child murders.

Piecing together sick stories with map references they paired unsolved murders with locations Percy admitted being in.

Before his death from cancer in 2013 at the age of 64, Percy told Sgt Newman he "couldn't remember" whether he killed a particular child or not. But he did recall being present near the site of particular murders on the relevant dates.

Percy only ever faced court for one murder - schoolgirl Yvonne Tuohy, 12, in 1969.

But detectives believed he could have been responsible for the child abductions and murders of eight other children - some of them the most notorious unsolved cases in Australian history.

Horrified, but intrigued, detectives began to match Percy's travels with his parents, on seaside caravan holidays and to the sailing regattas, with these unsolved crimes.

The result was a child murder map.

Old police identikit images of a man with a long lean face linked to a number of the crimes, were also strikingly similar to Percy.

TROUBLE AT AN EARLY AGE

Derek Percy had the hallmarks of a serial killer from an early age. He started stealing and wearing women's clothing, and developed a fetish for slashed or cut underwear and for knives.

Born in the inner-western Sydney suburb of Strathfield in 1948, he was the eldest of three surviving sons of railway electrician Ernest Percy and his wife, Elaine, a strong-minded housewife.

The trouble with Derek started the early 1960s when the intelligent but shy boy began engaging in odd behaviour.

Ernest Percy had taken his family to picturesque Mount Beauty in 1961 for his new job at the hydro-electric plant in Victoria's Kiewa Valley.

When women's underwear began disappearing from town clothes lines, the rumour was that teenage Derek was "snowdropping" as was the term for theft of that nature.

Two of Derek Percy's fellow students from Mount Beauty High School found him at a swimming hole wearing a woman's negligee and knickers.

When Percy's family moved to the tiny Snowy Mountains town of Khancoban in NSW for his father's new job, Derek stayed behind at Mount Beauty to finish his exams.

Derek stayed at the family home of his only school friend, Ken Hosking, who lived next door to the Casarotto family.

The Casarottos noticed their daughters' clothing had vanished from the clothesline.

Weeks later, a dumped suitcase was found with the clothing slashed and containing newspaper cut-outs of women in underwear with the faces, breast and genitalia cut from the pictures.

It was around this time that Percy began keeping his first diary, with graphic descriptions of his torture and rape fantasies.

In 1966, Percy joined his family in Khancoban and it was there that he lured two girls, aged five and six, to a caravan on the Percy property.

He managed to entice the children to show him their genitalia.

When they reported it to their parents, their father told Ernest and Elaine Percy. Ernest Percy dismissed the incident and told Derek to go and see the local doctor.

Whether a criminal charge or psychiatric counselling could have changed 17-year-old Derek Percy's course and saved lives is debatable, because if the detectives were right about Percy, the killing had already begun.

JANUARY 11, 1965: WANDA BEACH MURDERS

The Percy family holidays often coincided with yachting regattas and in January 1965 a national race was due to sail in Sydney.

Mount Beauty friends of the Percys remember they had gone to Sydney for a summer holiday staying with Derek's grandparents at Ryde station.

That month on Monday January 11 two Ryde teenagers set off from that station for a picnic at Cronulla beach.

Marianne Schmidt and Mary Sharrock, both aged 15, were neighbours and they headed off their day out with Marianne's four younger siblings.

A witness would later recall seeing a young man resembling Percy trying to talk with the girls on the train.

Marianne Schmidt (right, circled) in undated family photo with her parents and siblings on Wanda Beach in 1965. Photo / News Limited
Marianne Schmidt (right, circled) in undated family photo with her parents and siblings on Wanda Beach in 1965. Photo / News Limited

At Cronulla, the younger children stayed in a sheltered part of Wanda Beach, the furthest patrolled beach north on the Cronulla stretch.

Marianne's brother Peter Schmidt, 10, said later he saw Mary and his sister walking and talking with a long-haired blond youth.

The youth had a knife in a sheath and carried a spear. At that time Derek Percy was known to carry a knife in a scabbard.

Witness Wolfgang Schmidt, 7, also saw the boy accompany Mary and his sister into the sand dunes.

When the boy returned alone, Wolfgang said he asked where the girls were, but the youth walked on without replying. The beach party returned to Ryde without the girls.

The next day, Marianne and Mary's mutilated bodies were found partially buried in a sand dune.

Scratch marks on the girls faces showed they had fought for their lives.

The crotch area of one of the girls' bathers had been cut.

Marianne's brothers provided a description of the youth they had scene, and a police artist drew up a portrait of a man with a long, narrow face.

The following year at Percy's new school, Corryong High in Khancoban, fellow students who had seen a police sketch of the youth sought over the murders, teased him about being the killer.

In notes found in Percy's car four years later, police found a story written by Percy which bore a "striking similarity" to the Wanda Beach murders.

In his belongings in the tea chests they also found a map marked at Ryde near the spot where the Wanda Beach victims caught the train.

JANUARY 26, 1966 - BEAUMONT CHILDREN ABDUCTION

The day is writ in Australian crime history as the nation's loss of innocence, one of the greatest child abduction mysteries that still makes news today.

The three children of Jim and Nancy Beaumont: Jane, 9, Arnna, 7 and Grant, 4 caught the bus from their Somerton Park home for a short ride to Glenelg Beach, Adelaide.

The trip was meant to involve just a couple of hours at the beach, then home for lunch by midday. A family friend saw the trio at around 11am, talking a thin-faced man.

At 11.45am, the children bought a pie and two pasties from a bakery with a $1 note, almost certainly given to them because they had only been carrying coins.

The children were never seen again.

An Identikit of the man shows a long, clean-shaven face with light hair swept back.

The Beaumont children mystery has not gone away, with theories continually proposed and possible suspects identified.

The Beaumont parents believed for years their three children might still be alive but as the years rolled by and their marriage collapsed, no-one was charged with abduction or murder.

When questioned by police Derek Percy wouldn't admit to having anything to do with their abduction, but he did admit to being on Glenelg Beach that Australia Day in 1966.

As a coroner was to say about another child murder, it was not likely there were any other child molesters on the beach that day.

When police released this Identikit picture of the 1968 Simon Brook murder suspect, dozens of people phoned to say how similar it was to the Allen Redstone murder suspect.
When police released this Identikit picture of the 1968 Simon Brook murder suspect, dozens of people phoned to say how similar it was to the Allen Redstone murder suspect.

SEPTEMBER 28, 1966 - ALLEN REDSTON MURDER

Allen Geoffrey Redston, 6, was abducted on the way to a Canberra milk bar to buy ice cream.

The body of the little blond boy was found bound and hogtied the next day among reeds in Yarralumla Creek.

Wrapped in a green floral housecoat and several pieces of carpet, the boy had a piece of hempen rope looped around his neck.

Redston's bindings included a coarse piece of cloth with stripes similar to the colours of the Mount Beauty High School tie.

Derek Percy's fellow students remember him wearing a coarse, homemade version of the school tie in class.

A witness also described a suspect seen in the area where Allen Redston was abducted riding a red pushbike with distinctive handlebars.

Derek Percy had owned a similar bike in Mount Beauty and took it with him on holidays.

When Canberra Police issued a description of a blonde or fair thin-faced youth aged between 13 and 17 years that they wanted to interview, they also released an Identikit image.

The identikit closely resembled Percy.

Derek Percy later told police he has holidayed in the capital, but couldn't recall details.

A police investigation found that in the days leading up to the murder, a fair-haired teenager had been forcing boys to the ground, tying them up and placing plastic over their heads in an apparent attempt to asphyxiate them.

MAY 18, 1968 - SIMON BROOK MURDER

In late 1967 Derek Percy was accepted into the Australian Navy as a naval rating in electrical mechanics. After several months he was posted to the aircraft carrier HMAS Melbourne.

His ship was docked in Cockatoo Dry Dock on Sydney Harbour for a year-long refit, and the junior sailor assigned fire sentry duty. Percy lived at the naval base at nearby Garden Island and commuted through the suburb of Glebe to the dock.

On Saturday, May 18, 1968, Simon Brook, 3, went missing from the front yard of his family home in Alexandra Lane, Glebe, next to Jubilee Park.

Phyllis and Donald Brook believe Derek Percy murdered their son Simon, 3, in 1968. Photo / News Corp Australia
Phyllis and Donald Brook believe Derek Percy murdered their son Simon, 3, in 1968. Photo / News Corp Australia

A truck driver later said he'd seen a boy matching Simon Brook's description holding a young man's hand near Jubilee Park.

The mystery man was well-groomed with a neat haircut, and the Identikit image was also startlingly similarity to a photograph of Percy as a schoolboy.

The little boy's body was found behind a building site. His mouth was stuffed with wads of newspaper, his throat was slit, his trousers removed and his lower body mutilated.

At the crime scene police found two Gillette razor blades, the same brand the navy issued to sailors.

Later, in Percy's diaries, police found a story about the abduction and killing of a three-year-old whose genitalia was severed with a razor blade.

Asked whether he had killed Simon Brook, Percy would only say he "could have" and that he been in the Glebe area at the time.

Simon Brook's parents, Phyllis and Donald Brook, were satisfied Derek Percy was their son's killer.

However when a 2005 inquest into the boy's death ended after two days with a recommendation that Percy be charged, the NSW Director of Public Prosecutions, Nicholas Cowdery declined to proceed.

After Percy's 2013 death, Professor Brook told Fairfax "The thing about the lapse of time in relation to grief is not that grief diminishes it, just that it comes upon one less frequently.

"It's still there in just the same. The only thing that's gone away is the danger of Percy to small children."

AUGUST 10, 1968 - LINDA STILWELL MURDER

Percy had transferred to the troop ship HMAS Sydney, which was based in Melbourne, on July 1, 1968, but was on leave for 18 days from August 5, five days before the abduction of Linda Stilwell.

The Stilwell family had migrated from England three years earlier, but by the middle of 1968 parents Brian and Jean had separated.

Brian took the youngest of their four children, Laura, to New Zealand.

Mrs Stilwell found a job at the Albert Park Hotel and cared for the three others, Karen, 11, and Gary, 9 and Linda, 7.

On August 10, 1968, a Saturday, Jean told her children to stay indoors in their flat while she went grocery shopping.

Karen and Gary couldn't resist going to the beach, and when Mrs Stilwell returned at around midday, she told Linda to go and fetch them for lunch.

Karen returned to say that Gary and Linda were fishing on St Kilda pier, about 2km from their home.

At 4pm, Gary returned to say that Linda had gone with some boys to a local attraction known as Little Luna Park.

When she sent him out again to get Linda, he returned to say she had gone with the boys to the police station to pick up some fishing rods.

Jean Stilwell rang the police to learn that three boys had attended the station, but there was no sign of a little girl.

Karen, Gary and Linda Stilwell (right), a few months before Linda's abduction. Her body has never been found.
Karen, Gary and Linda Stilwell (right), a few months before Linda's abduction. Her body has never been found.

Two days later a witness told police she had seen a little girl rolling on a grassy bank near the pier.

The woman said a man had been sitting with the girl. She described him wearing "a deep navy blue, almost black, spray jacket, similar to that worn when sailing. The man was sitting with his legs crossed looking out to sea quite intently".

The following year, the woman would open the newspaper to look at a photograph of the suspect in the Yvonne Tuohy murder.

She would say, "I got the biggest shock of my life. This was the same man that was sitting on the park bench the day that the little Stilwell girl disappeared in St Kilda".

More recently, after Percy was questioned in the Melbourne Magistrates Court following the discovery of the secret cache of his papers, she came forward again to say, "I am absolutely sure that the man I saw sitting on the park bench the day Stilwell disappeared is the same man."

When Percy was asked about Linda's disappearance, he said he had driven through St Kilda that day.

A coroner later found Linda Stilwell had met with foul play and that Derek Percy had murdered her.

"It is highly unlikely that another child molester was in the vicinity when Linda disappeared," Victorian Deputy State Coroner Iain West found.

Linda Stilwell's brother Gary said the family had been through "hell" since the murder.

"The last 46 years have been a terrible thing on my mother and the rest of the family," he told the ABC.

"It's now been proven that Derek Percy preyed on Linda and other innocent children."

Derek Percy, 21, re-enacts for police the murder of Yvonne Tuohy, 12, showing them how he used to keep the murder knife in his car seat. Photo / News Corp
Derek Percy, 21, re-enacts for police the murder of Yvonne Tuohy, 12, showing them how he used to keep the murder knife in his car seat. Photo / News Corp

APRIL 1, 1969 - ATTEMPTED ABDUCTION

In 1969, Percy was stationed on the HMAS Cerberus, the Royal Australian Navy's primary training establishment on Westernport Bay, Victoria 90km southeast of Melbourne.

On April 1, he attempted to abduct a 12-year-old girl on a bike near the Cerberus base, but she got away from him.

A terrible incident just four months later would give the girl cause to identify Percy as her attacker.

JULY 20, 1969 - YVONNE TUOHY MURDER

In effect there were two victims on that crisp winter's day in Warneet, a tiny town on the coast of Westernport Bay in July 1969.

Shane Spiller, 11 was on holiday from Melbourne.

He and his friend, Yvonne Tuohy, 12, were walking down a dirt track on their way to Ski Beach to make a fire of driftwood and have a picnic.

Suddenly a man came over and grabbed Yvonne, holding a red dagger to her neck.

When he tried to beckon Shane to come with them, the boy pulled the tomahawk from his belt that he had brought to cut the driftwood.

Percy said, "put that down or else I'll hurt the girl".

Yvonne cried out, "Shane, help, help. He's going to cut my throat."

Spiller ran through scrub to the road and saw Percy's car drive past with Yvonne under a blanket.

Eleven-year-old Shane Spiller with his tomahawk after trying to ward off Derek Percy, who murdered his friend Yvonne Tuohy. Photo / News Corp
Eleven-year-old Shane Spiller with his tomahawk after trying to ward off Derek Percy, who murdered his friend Yvonne Tuohy. Photo / News Corp

When Spiller was interviewed by police he identified the make and colour of Percy's car, an orange station wagon with a sticker on the rear window.

The sticker, which Spiller drew for police, had a Royal Navy emblem. Police went to the Cerberus Navy base and found Percy washing blood off his clothes.

For the first time in what detectives believe was his long murder spree, the paedophile sadist had been caught red-handed.

Percy denied all knowledge of the murder, but admitted he had been on Ski Beach.

Eventually, he took police to Fisheries Road, Devon Meadows, 8km from where he had abducted Yvonne.

Her body was under some bushes. The girl had her wrists behind her, her mouth stuffed with a balled cloth and Percy had strangled her and mutilated her body with long, deep cuts.

Shane Spiller was forced to identify Percy in a line-up with terrible consequences.

Newspapers featured photos of him holding his tomahawk. If he was feted as a hero, he didn't feel like one.

In 1970, Percy was convicted of Yvonne Tuohy's murder but found not guilty by reason of insanity. Much later, psychiatrists would later find Percy was not mentally ill at all.

But it was too late by then for Shane Spiller, by age 14 had begun drinking and drifted away from school and his family.

Spiller developed serious drug and alcohol addictions and was never properly treated for a severe case of post traumatic stress disorder.

He believed Derek Percy would come after him and kill him.

Spiller ended up in the NSW South Coast town of Wyndham, where he slept with a baseball bat and cut a trapdoor into his living room floor to hide.

He would ask friends to jot down the registration numbers of cars in his street.

"He was the most paranoid person I've ever met," neighbour Andy Morris told Fairfax.

"There was this overwhelming dark cloud over his life and he was basically self-medicating with drugs and alcohol."

On September 9, 2002, he was seen leaving his two-room shack for the local store to collect his mail. He has not been seen alive since, nor have his remains been found.

Wyndham locals recognised Spiller's bravery on that day back in Warneet, but the fallout was tremendous.

"In a sense, Shane was a Derek Percy murder victim as well. To me, he was a very brave man," Andy Morris said.