Derek Ernest Percy (15 September 1948 - 23 July 2013) was an Australian child killer, linked to the mysterious deaths of nine children in the 1960s.
Percy was born on September 15 1948 in Strathfield, New South Wales, the eldest of three sons of parents Ernest and Elaine Percy. His father had been a New South Wales railway electrician before deciding to take a job with the State Electricity Commission in Victoria, and moving to Chelsea, then to Warrnambool in 1957, and to Mount Beauty, near Bright in 1961. Percy began to attract the attention of authorities in late 1964 as a 16 year old boy when he started stealing and wearing underwear and mutilating dolls with razor blades and knives. In 1965, the family relocated to Khancoban in New South Wales, where he began writing down bizarre and violent sexual fantasies. In 1966, he repeated year 11, then tried year 12, but dropped out and joined the navy as a naval rating in electrical mechanics in November 1967. He was posted to the aircraft carrier HMAS Melbourne in March 1968, HMAS Sydney (based in Melbourne) on 1 July 1968, and HMAS Cerberus naval base in April 1969.
Percy was arrested at Cerberus, adjacent to Crib Point on the Mornington Peninsula, south of Melbourne, for the murder of 12 year-old Yvonne Tuohy at Ski Beach, near Warneet on Westernport Bay, on 27 July 1969. At the time he abducted Tuohy at knife-point, he also tried to abduct her friend, Shane Spiller, 11, who only escaped by threatening Percy with his tomahawk. Spiller, however, was able to describe to police the abductor and his vehicle, an orange Datsun station wagon with a navy sticker on the back window. Police then went to the Cerberus base and discovered Percy washing blood off his clothes. When questioned, he denied involvement, but eventually led police to her body on Fisheries Road at Devon Meadows, some 8 kilometres (5 mi) from the abduction scene. In 1970, he was found not guilty, by reason of insanity, of the murder of Tuohy, and remanded indefinitely.
Due to the nature of the attack, and based on documents in his possession, he also became a suspect in the Wanda Beach Murders and the Beaumont children disappearance, and in the individual murders of Allen Redston in Canberra in 1966, Linda Stilwell in St Kilda in 1968 and Simon Brook in Sydney in 1968. He repeatedly stated that he could not remember whether or not he had committed any further crimes. Detectives then started trying to piece together his movements around Australia at the time of the murders. They were aware the family often took caravan holidays during yachting regattas near beaches (where most of the crimes took place), that his transfers within the navy brought him close to many of the crime scenes, and knew that Percy was harbouring paedophilic and psychopathic fantasies towards children. In 2007, a cache of 35 boxes of Percy's diaries, drawings, and newspaper clippings was found in a storage unit in South Melbourne, casting further suspicion on him.
Based on these facts, investigators continued to pursue the following leads for nearly half a century:
Percy died from lung cancer in St Vincents Hospital, Melbourne on 23 July 2013, aged 64, without admitting to any further crimes. At the time he was the longest serving prison inmate in Australia, some 44 years.