How many kids did he murder?

Deputy State Coroner Iain West and Detective Senior Sgt Wayne Newman interview Derek Percy over the 1968 murder of Linda Stilwell

Linda Stilwell, seven, went missing from the St Kilda foreshore near Luna Park in August 1968. Source: Supplied

DEREK Percy was Australia's real life bogeyman.

The former naval sailor has been linked to the murders and disappearances of at least nine children in three states, including the Beaumont children, whose fate remains one of this country's most enduring mysteries.

The Beaumont children vanished on Australia Day in 1966 Source: Supplied

Despite evidence placing him near the scene of each crime, Percy managed to escape conviction in all but one case, leaving relatives in never-ending limbo.

This morning, a coroner offered Jean Priest, the mother of Linda Stilwell, some comfort after finally ruling that Percy caused her daughter's death 46 years ago.

Victorian Deputy State Coroner Iain West had already declared, at a previous hearing, that Percy had been seen in St Kilda on August 10, 1968, the day seven-year-old Linda went missing from the foreshore near Luna Park.

Jean Priest, the mother of Linda Stilwell who went missing in 1968. Source: News Limited

Ms Priest had been fighting for years to force Percy, who died last year, to give evidence at inquest. After losing one of those legal battles, she was ordered to pay Percy's court costs.

Percy was convicted of the abduction, torture and murder of 12-year-old Yvonne Tuohy, who was snatched from a beach at Victoria's Westernport Bay in July 1969. He was arrested hours later, and was found to be criminally insane and jailed indefinitely.

Since then, investigators have tried every trick in the book to get Percy to admit his role in at least eight other high profile crimes involving children.

An attempt to extract a deathbed confession as Percy lay dying from lung cancer at St Vincents Hospital in Melbourne failed, with the old man maintaining a stony silence until he drew his last breath.

Derek Percy, as he appeared in a police mugshot after his arrest for the murder of Yvonne Tuohy, 12, in 1969. Source: Supplied

When Percy was arrested over the Tuohy case, he was also investigated in connection with Linda's disappearance. Police found maps, one with a line drawn past the spot on the St Kilda foreshore where Linda was last seen. A witness told police she saw the little girl near a man wearing a dark spray jacket. When Percy was arrested for murder of Yvonne Tuohy, he was photographed wearing the same style of jacket.

Mr West would subsequently rule that Percy would not be a reliable witness and could not be compelled to testify. That decision was effectively overturned last December when the Victorian Court of Appeal said Percy should have been offered immunity to give evidence.

Christine Sharrock and best friend Marianne Schmidt, both 15, were killed at Wanda Beach in 1965. Source: News Corp Australia

It is widely-believed that Percy was behind the still-unsolved Wanda Beach murders near Cronulla in Sydney's Sutherland Shire in 1965.

Best friends and neighbours Christine Sharrock and Marianne Schmidt, both 15, disappeared on January 11 during a trip to Cronulla Beach with Marianne's younger siblings.

The teenagers became separated from the younger children some time that afternoon. Their bashed and mutilated bodies were found partially buried in the sand dunes of nearby Wanda Beach the following day.

In 2007, Victoria Police questioned Percy in jail after discovering 35 boxes of documents in a storage unit. It was later established their contents included Percy's possessions at the time of his arrest as well as material smuggled out of jail from the 1970s onwards.

One contained a handwritten note saying "Wanda". They also found a street directory containing handwritten marks around St Kilda Pier, the area Linda Stilwell was abducted from.

Another crucial piece of circumstantial evidence were several packets of razor blades similar to those police believe were used to mutilate Christine and Marianne and later, Yvonne Tuohy.

At the time of the murders, Percy had been staying with his grandmother in Ryde, where the girls also lived.

Percy as he looked in the months before his death in Melbourne last year. Source: Supplied

Percy has also been linked to the mysterious disappearance of the Beaumont children, who vanished from the Adelaide suburb of Somerton Park on Australia Day 1966.

Jane, nine, Arnna, seven, and Grant, four, left their home at around 10am to catch the bus to nearby Glenelg Beach.

They were expected to catch the midday bus back home but never returned.

The case remains unsolved.

The Beaumont children have never been found. Source: Supplied

Percy was stationed in Sydney with the navy in 1968 when three-year-old Simon Brook was kidnapped and murdered.

The little boy had been seen playing in the front yard of his Glebe home and spotted wandering off with a "thin-faced" man.

Percy was in Sydney when Simon Brook was kidnapped from his Glebe home and murdered. Source: Supplied

In 2005 a coronial inquest recommended Percy be referred to the Director of Public Prosecutions over Simon's murder but the then-DPP, Nicholas Cowdery decided there was insufficient evidence to press ahead.

An inquest has found convicted killer Derek Percy responsible for seven-year-old Linda Stilwell's death.

Percy has also been linked to the murder of six-year-old Allen Redston, who was found dead next to a creek bed in the Canberra suburb of Curtin on September 28, 1966.

His mother had sent him to the shops to buy ice cream for his brother and himself.

Detectives interviewed several men in Queensland over the crime but nobody has ever been convicted of his murder.