It happened on a popular Sydney beach way back in 1965. Two teenage girls - Marianne Schmidt and Christine Sharrock – were sexually assaulted, murdered and partially buried in the sand dunes. For a shocked nation, it was a loss of innocence. For fifty years, investigators asked, who could commit such a crime? Yet police had him - and the courts let him go. He went on to become one of the worst serial killers in modern history.