On June 4, 1961, Australian detectives were summoned to the Sydney Domain Baths, where a man's nude, mutilated body had been found beneath the dressing sheds. The victim , Alfred Greenfield, had been stabbed a minimum of 30 times, his genitals hacked off, and homicide investigators pegged the crime as a homosexual assault. Their suspicions were confirmed when the killer left his second victim, William Cobbin, stabbed repeatedly and mutilated in a public restroom at Moore Park.

Investigators were scouring homosexual hangouts, searching for possible witnesses, when a third victim was savaged in suburban Darlinghurst, on March 31, 1962. Frank Mclean was still alive when found, but he died from his wounds a short time later, without providing a description of his killer.

In mid-November, merchants in suburban Concord filed complaints of rancid odors emanating from a shop purchased by William MacDonald two weeks earlier. The new tenant had not been seen since November 4, and searchers were convinced that he had fallen victim to the "Sydney Mutilator" when they found a naked, butchered corpse concealed beneath the shop. The latest victim had been stabbed 41 times, his genitals slashed, but a new twist was added to the case when police examined clothing found beside the body, tracing a laundry mark back to its source. In time, the victim was identified as an Irishman, Patrick Hackett, and the search for William MacDonald resumed.

On April 22, 1963, a former co-worker sighted MacDonald on a Sydney street. A month later, he was traced to his new job, in a Melbourne railway station, where he had been hired as "David Allan." Under questioning, MacDonald confessed his identity along with the series of murders, blaming the crimes on an irresistible compulsion. Traumatized by a homosexual rape in his teens, the slayer was driven to seek revenge against gays selected at random. Sentenced to life on conviction of murder, MacDonald was later transferred to the Morriset Home for the Criminally Insane.