In the history of Australian true crime, few cases have
raised such disturbing questions about criminal responsibility, investigative
evidence and the limits of justice as the case of Derek Ernest Percy.
Percy was convicted in connection with the brutal
1969 murder of 12-year-old Yvonne
Tuohy. Yet
the legal outcome was extraordinary: he was found not guilty by reason of insanity and detained indefinitely.
Investigators later examined possible links between him and several other
missing-child and murder cases, but those suspicions did not all produce
conclusive evidence.
That distinction matters. Percy became one of the
most controversial figures in Australia's criminal justice system, not simply because of the crime
for which he was detained, but because of the unanswered questions that
followed him for decades.
The story began in a seemingly ordinary coastal
community, where two children set out for a picnic and one of them never came
home.
A Walk to the Beach That Ended in
Horror
Warneet, a small township on the shores of Western
Port Bay, lies roughly 60 kilometres southeast of Melbourne. In 1969, it was a
familiar destination for families, anglers and holidaymakers. Children often
played outdoors with little supervision, and a walk to the beach seemed like an
ordinary afternoon adventure.
On the day of the abduction, 11-year-old Shane
Spiller collected his 12-year-old neighbour, Yvonne Tuohy. He carried a small
tomahawk intended for chopping kindling for a beach fire.
Neither child had reason to expect danger.
As they walked along a track towards the shore, they
passed a parked car. The driver was 21-year-old Derek Percy, a naval cadet
stationed at HMAS Cerberus. According to the account later given to
investigators, Percy suddenly got out and grabbed Yvonne.
He also called Shane towards him.
The boy raised his tomahawk and threatened to strike
Percy. The man backed away from Shane but continued holding Yvonne. Realising
he could not overpower the adult, Shane ran to find help.
As he fled, he heard Yvonne cry out. He later
recalled hearing words suggesting that Percy intended to cut her throat.
That moment would remain central to the
investigation—and to Shane's life.
The Small Detail That Helped
Police Find the Suspect
One of the most important details Shane remembered
was not a face or a name. It was a naval identification sign on the vehicle.
Police officers took the boy to HMAS Cerberus, where
he identified a Datsun 1000 in the car park. Detectives Ken Robertson and
Delaney travelled from Melbourne and began tracing the vehicle to its owner.
Their inquiries led them to Percy.
According to former detective Ken Robertson, officers
found Percy washing bloodstained clothing when they went to his room.
Investigators obtained permission from the naval base commander to take him to
a police station for questioning.
At that stage, the immediate priority was finding
Yvonne. Percy appeared quiet and cooperative, but Robertson later recalled
being troubled by the suspect's apparent unwillingness to provide useful
information.
The formal interview took place at Frankston police
station. Sergeant Dick Knight led the questioning and asked Percy to retrace
his movements from the naval base to Warneet.
The account says Percy eventually confessed to
abducting and killing Yvonne and offered to guide police to her body.
He directed officers to an area near Fisheries Road
in Devon Meadows, several kilometres from the abduction site.
What investigators found there was devastating.
Yvonne's body had been left behind bushes, bound and gagged. The condition of
the remains deeply affected the officers who attended the scene.
Robertson, who had spent years working in homicide
investigations, later described the discovery as one of the most disturbing
experiences of his career.
For Yvonne's family, the discovery brought an answer
to the question of where she was—but no relief from the loss.
The Diary That Raised Questions
About Earlier Crimes
The investigation took a wider turn when police
examined Percy's belongings at HMAS Cerberus.
Among the material was a diary containing disturbing violent and sadistic fantasies. Some entries described the
murder and mutilation of a very young boy.
Detectives in New South Wales recognised similarities
between those descriptions and the 1968 killing of three-year-old Simon Brook in Sydney.
Simon had been playing in the backyard of his
family's home in Glebe. The property backed onto Jubilee Park. During a visit
from family friends, the adults went inside, and the child disappeared.
A search began immediately. The following day, his
body was discovered in dense vegetation behind a partly constructed building on
Glebe Point Road.
The circumstances were horrific. The child had been
suffocated, and his body had been mutilated.
Percy had been serving in the Navy at Garden Island
in Sydney around that period. He knew the Glebe area through his family and was
reportedly on leave on the day Simon disappeared.
After Yvonne's murder, Percy spoke to an old school
friend, Ron Anderson, who was then a police officer. According to Anderson's
later account, Percy made a remark suggesting that he had made a serious
mistake this time.
Investigators considered the comment, his diary and
his movements relevant to the Simon Brook inquiry.
But suspicion is not the same as proof. The available
evidence did not establish a criminal conviction against Percy for Simon's
death.
That distinction would become one of the defining
problems in the decades-long effort to determine whether Percy was responsible
for other crimes.
Linda Stillwell: Another
Disappearance Near the Coast
A further case attracted investigators' attention:
the disappearance of seven-year-old Linda Stillwell
from St Kilda in 1968.
Linda had gone to the beach with her siblings. At
some point, the children became separated. Her older brothers and sisters
returned home, apparently believing she was following them.
She never arrived.
Victoria Police launched an extensive search, but no trace
of the child was found.
After Percy's arrest for Yvonne's murder, Anderson
questioned him about Linda. Percy reportedly acknowledged that he might have
been driving through St Kilda on the day she vanished, but said he could not
remember anything more.
That answer became familiar to investigators over the
years.
Percy repeatedly claimed that his memory was
incomplete. Police and families seeking answers were left with a frustrating
combination of suggestive statements, circumstantial details and missing
evidence.
The case remained unresolved for decades.
The 1970 Insanity Verdict That
Divided Australia
Percy pleaded not guilty to Yvonne's murder on the
grounds of legal
insanity.
In 1970, the jury found him not guilty by reason of
insanity. The court ordered that he be detained at the governor's pleasure,
meaning he had no ordinary release date.
The verdict became controversial.
Some investigators believed Percy understood the
nature of his actions and knew they were wrong. They argued that the detailed fantasies
recorded in his writings suggested planning and awareness, and they questioned
whether the insanity finding adequately reflected his responsibility.
Others took a different position. They argued that
the psychiatric evidence supported the verdict and that indefinite detention
protected the public.
The disagreement was not merely about terminology. It
raised difficult questions about how the law should treat people whose mental
condition is considered to have affected their criminal responsibility.
Under the legal framework applied at the time, the
verdict meant Percy was not convicted of murder in the ordinary sense. That
distinction also had practical consequences for later investigations.
Police could not simply treat him as a convicted
murderer when seeking certain forms of evidence. In particular, the absence of
a murder conviction complicated efforts to obtain a DNA sample from him.
For families connected to other unsolved cases, the
legal outcome created another obstacle in an already difficult search for
answers.
A Disturbing History Before the
Murder
Psychiatrists and investigators later examined
Percy's childhood and teenage years in an attempt to understand how his
behaviour developed.
He grew up in an apparently ordinary Australian
family. His father, Ernest, was described as strict and frequently away for
work. His mother was protective, and Percy was reportedly a solitary child who
formed few close relationships.
Accounts from Mount Beauty in northern Victoria
described troubling behaviour during his adolescence.
Women's clothing and underwear reportedly disappeared
from neighbourhood properties. Two school friends later described seeing Percy
in the bush wearing stolen clothing and cutting up underwear.
There were also accounts that he had molested two
young girls in a caravan. His father reportedly promised their parents that
Percy would receive help, but the family subsequently moved away.
According to later accounts, Ernest Percy discovered
his son's disturbing writings and destroyed the diaries rather than confronting
him.
Forensic psychiatrist Professor Paul Mullen later
wondered whether earlier intervention might have changed the course of events.
It is impossible to know what would have happened if
Percy had received effective treatment or supervision during adolescence.
Nevertheless, the history raised questions about early intervention, the handling of troubling
behaviour and the responsibilities of adults who become aware of serious
warning signs.
Life Behind Bars: A Prisoner Who Revealed
Almost Nothing
Percy was initially held at Pentridge Prison in
Melbourne, where he was placed in G Division, a unit for prisoners who did not
fit easily into the usual classifications.
Despite the severity of his case, accounts suggest
that he adapted to the institution's routines. He eventually became influential
within the division, helping organise aspects of daily prison life.
A former inmate later described him as unremarkable
and difficult to read.
More than two decades into Percy's detention,
Professor Paul Mullen began assessing him. The psychiatrist found it difficult
to establish a meaningful connection.
Percy was guarded and emotionally difficult to reach.
Mullen gradually built conversations around subjects that interested him,
particularly Test
cricket, a
sport Percy reportedly followed in extraordinary detail.
The hope was that trust might eventually lead to a
better understanding of his thinking and behaviour.
It did not produce the answers investigators wanted.
Percy continued to avoid discussing the crimes and
the wider questions surrounding his past. His writings, meanwhile, remained a
source of concern.
A prison-related group had arranged for material
written by Percy to be taken outside the institution and stored. The
arrangement continued for years.
Then, in 2007, a remarkable discovery brought the
case back into public attention.
The 35 Boxes That Reopened
Australia's Cold Cases
Thirty-five boxes of Percy's diaries and related
documents were discovered in a Melbourne self-storage facility.
The material attracted renewed interest because it
appeared to offer a rare window into the mind of a man connected to one
confirmed child murder and suspected in several other investigations.
For cold
case investigators,
the discovery raised an obvious question: could the writings help establish
whether Percy had been involved in other disappearances and killings?
Among the cases discussed were the 1965 Wanda Beach
murders, the disappearance of the Beaumont children and the killing of
six-year-old Allen Reston.
Each case had its own history, evidence and
unanswered questions. None could responsibly be attributed to Percy simply
because investigators found his writings disturbing.
The Wanda Beach Murders
In 1965, two 15-year-old girls were attacked and
killed at Wanda Beach in Sydney. Their bodies were later found buried in the
sand dunes.
Investigators considered whether Percy could have
been in the area. His grandmother reportedly lived in a neighbouring suburb,
giving police a possible reason to examine his movements.
However, researchers questioned the theory. They
pointed to the lack of direct evidence and doubts about whether Percy's known
behaviour and circumstances fitted the crime.
No conclusive evidence established that he murdered
the two girls.
The Beaumont Children
The disappearance of Jane, Arna and Grant Beaumont
remains one of Australia's most famous missing children cases.
On Australia Day in 1966, the three siblings disappeared
from Glenelg Beach in Adelaide. They were aged nine, seven and four.
Percy reportedly told Anderson that he believed he
had been at the beach that day.
But a reported family account suggested that the
Percys' visit to Adelaide may have been limited to a cruise stop and a visit to
the Adelaide Oval.
Researchers also questioned whether a teenager
travelling with his parents could realistically have carried out the abduction
and concealed the children.
The theory remains unproven. There is no established
evidence that Percy was responsible for their disappearance.
The Death of Allen Reston
Six-year-old Allen Reston was found dead in a
Canberra suburb. He had been bound and suffocated, and his body had been
wrapped in old cloth.
Investigators focused on a teenager reportedly seen
riding a red bicycle.
Percy's circumstances at the time did not appear to
fit that description particularly well. His family was living in Cooma,
hundreds of kilometres away.
As with the other cases, the available material did
not establish his involvement.
The distinction between a possible investigative lead
and a proven crime is essential. The discovery of the 35 boxes reopened
questions, but it did not provide a reliable answer to every mystery.
Why the Simon Brook Investigation
Could Not Deliver a Conviction
Simon's family continued pressing authorities to
investigate whether Percy had been responsible for the child's death.
In 2000, Simon's father, Donald, asked New South
Wales Police whether DNA testing could help establish the truth.
The effort faced major difficulties. Much of the
original crime-scene evidence had reportedly been destroyed, and Percy's legal
status created further complications around obtaining a sample.
A second coronial inquest examined the case. Percy
was brought before the proceedings, but he offered little useful information.
There was no decisive forensic evidence linking him
to Simon's death.
The inquiry therefore could not produce the
conclusive finding the family wanted.
Donald Brook nevertheless acknowledged the efforts of
police and the courts to pursue the case.
For families living with an unsolved murder, even a
renewed investigation can bring painful memories back without providing the
certainty they have spent years seeking.
Shane Spiller: The Survivor Who
Never Escaped the Memory
The story of Yvonne's abduction did not end with
Percy's detention.
Shane Spiller, the boy who ran for help, carried the
memory of that day into adulthood.
People who later knew him described him as friendly
and gentle, but also anxious and vulnerable. He lived in a small community
where neighbours looked out for him.
Retired detective sergeant Mark Winterflood met Shane
in the late 1990s. He recalled a man who was easy to talk to but appeared deeply
troubled.
As Percy began seeking release through custodial
reviews, Shane reportedly became increasingly fearful.
He believed Percy might arrange for someone to harm
him from prison. Police investigated the concern, including a search of Percy's
cell, but found no reference to Shane.
There was no evidence establishing that Percy had
ordered a threat against him.
Shane's fears were nevertheless real to him, and his
distress became increasingly serious.
He made repeated attempts to harm himself and was admitted
to hospital. A few days after his final discharge in 2002, he disappeared.
Winterflood investigated and considered several
possibilities, including suicide, an accidental overdose followed by an attempt
to conceal the death, or homicide. He regarded homicide as the least likely of
the three.
No trace of Shane or his remains was found.
His disappearance added another unresolved tragedy to
a case already marked by loss.
Many observers have described Shane as the person
whose quick thinking helped police identify Percy. He noticed the naval sign on
the car, escaped to find assistance and later identified the suspect.
But the experience also placed a terrible burden on a
child.
He had to identify Percy in person and later appear
at the trial. For those who knew him, the repeated exposure to the man who had
abducted Yvonne was an especially painful part of his story.
Linda Stillwell's Family Refused
to Give Up
Linda's mother, Jean Priest, continued seeking
answers long after her daughter's disappearance.
In 2009, a second inquest into Linda's case was
ordered. Priest then spent years pursuing an opportunity for Percy to be
questioned.
At first, the coroner declined to compel him to
testify. The decision was deeply frustrating for the family.
Another controversy arose when Percy sought
approximately $32,000 in legal costs. The request attracted public criticism,
particularly because he had accumulated money during his detention, including
through a Navy pension.
The state government eventually accepted responsibility
for the legal costs.
At the inquest, witness Edith Jamison described
seeing a man sitting on a bench near the St Kilda foreshore on the day Linda
disappeared. She said she had felt uneasy about the way he appeared to be
watching the child.
After Percy's photograph appeared in newspapers
following Yvonne's murder, Jamison believed she recognised him as the man she
had seen.
Anderson also gave evidence. He described Percy's
earlier statement that he might have been in the area but could not remember
more.
The evidence did not include a confession.
Nevertheless, investigators continued examining
Percy's movements and the material recovered from his possession.
The Deathbed Interview That
Changed Linda's Case
By this stage, Percy was seriously ill with cancer
and had been in detention for more than four decades.
As his condition deteriorated, he eventually agreed
to be questioned by Detective Wayne Newman and Deputy State Coroner Ian West.
The interview took place at St Vincent's Hospital.
Investigators presented Percy with a road atlas that
had been found among his belongings at the time of his 1969 arrest. Markings on
the map reportedly corresponded with the area where Linda had last been seen.
The detail was significant because it appeared
consistent with information Percy had previously given Anderson.
But Percy still did not confess to killing Linda, nor
did he reveal the location of her body.
The interview provided another piece of evidence for
the inquest, but it did not end every uncertainty.
In 2014, the deputy state coroner found that Percy
had abducted and killed Linda Stillwell in 1968.
For Linda's family, the finding represented a measure
of recognition after decades of uncertainty. They embraced as the conclusion
was delivered.
Yet there was still no body, and the family had to
live with the fact that some questions could never be answered.
Percy died in 2013, after spending approximately 43
years in detention. He was one of Victoria's longest-serving prisoners.
Could Percy Ever Have Been Released?
Percy applied for custodial reviews, including an
application in 1998 after nearly three decades in detention.
Mullen was involved in assessing him.
The psychiatrist later said he would not have
recommended release. He could not be confident that Percy posed no danger to
the public, and he believed the potential consequences of getting that decision
wrong were too serious.
The issue highlighted a central challenge in forensic psychiatry and the management of high-risk
offenders: how can authorities assess whether someone who committed an
extremely serious crime decades earlier remains a danger?
A long period in custody does not automatically
demonstrate that risk has disappeared. Nor does a psychiatric assessment
provide perfect certainty about future behaviour.
In Percy's case, the authorities ultimately kept him
detained until his death.
The Question That Still Divides
the Case
Derek Percy's story continues to provoke debate
because it sits at the intersection of several difficult issues:
·
Criminal
responsibility:
Did the insanity verdict accurately reflect his mental condition and legal
responsibility?
·
Victim
justice: Did
the legal outcome provide sufficient recognition and accountability for
Yvonne's family?
·
Cold
case evidence:
How much weight should investigators give to diaries, suspicious statements and
circumstantial links?
·
Forensic
investigation:
Could modern DNA testing have resolved cases if more original evidence had
survived?
·
Public
safety: Was
indefinite detention the only responsible way to manage the risk Percy
presented?
There is also the question of how many crimes he
actually committed.
Percy was convicted in connection with Yvonne's
murder through the 1970 insanity finding, and the later coronial finding
attributed Linda Stillwell's death to him. Other cases were investigated, but
the evidence did not establish his responsibility for every disappearance or
murder discussed in connection with his name.
That distinction should not be lost amid the
disturbing details.
The Beaumont children, the Wanda Beach victims, Simon
Brook and Allen Reston each deserve to be remembered as individuals, not simply
as names in a theory about one notorious offender.
A Case Defined by Answers—and by
What Remained Unknown
For Yvonne Tuohy's family, the investigation
identified the man responsible for her death. For Linda Stillwell's family, the
later coronial finding brought a long-awaited measure of recognition.
But Simon Brook's case did not produce a definitive
criminal finding against Percy. The disappearance of the Beaumont children
remains unresolved. Shane Spiller also vanished, leaving his own family and
community without answers.
Perhaps the most haunting part of the story is not
the nickname later attached to Percy or the descriptions of his personality. It
is the number of people whose lives were changed by the events of those years.
A boy noticed a small sign on a car and ran for help.
A family spent decades searching for a missing child. Detectives revisited old
evidence, psychiatrists tried to understand a deeply disturbed prisoner, and
coroners were left to assess what could still be proved.
Percy died without providing the answers many
families wanted.
His case remains a sobering chapter in Australian criminal history—a reminder that even when
investigators identify an offender, the wider search for truth can continue for
generations.
Editorial note: This article distinguishes established legal outcomes and coronial findings from allegations and investigative theories. Percy was not proven responsible for every unsolved case discussed above. The disappearance of Shane Spiller and several other cases remain unresolved.
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