Fact, Conjecture, Speculation and the Unsolved Murders of Marianne Schmidt and Christine Sharrock

On 11 January 1965, 15-year-old best friends, Marianne Schmidt and Christine Sharrock were overwhelmed and slaughtered in the sandhills behind Sydney's Wanda Beach. Not only had the killer struck in a public area and during the summer school holiday break, but he'd done it in broad daylight. Despite the brazenness of the act, several police investigations and their ostensibly ongoing inquiries have failed to bring the killer to justice. Why did Marianne and Christine walk into the sandhills that ill-fated day? Why were they killed? How did their killer, who was almost certainly blood soaked, leave the area unseen? Why have the various police investigations failed to identify the killer? Were Marianne and Christine early victims of a 'True Crime Anti-Hero' like the vile Derek Percy, or the sadistic Christopher Wilder? Were they victims of a sexual assault gone awry, or were they the 'gateway' victims of a short-lived 'ripper-esque' killing spree in the Sydney-Wollongong corridor?