Gustav Carl Friedrich Müller was born in 1865 somewhere in Germany, the son of a foreman with the Prussian state railways. Much of his early life remains undocumented, but by 1888, he had married a woman in Berlin and fathered a son. Despite working as a skilled watchmaker and gold miner, Müller went bankrupt in January 1890, prompting him to abruptly abandon his family. From that point, he became a global drifter, crossing continents and reportedly marrying multiple women under false pretenses.

His nomadic years brought him through India, where he was injured falling from an elephant and later treated in a hospital for epileptic seizures and mental instability. He claimed this accident marked the beginning of his psychological decline. By March 1893, Müller made his way to England, where a police officer found him aimlessly wandering Southwark. Speaking only German, Müller claimed to have killed his parents, wife, and thousands of others, including children.

He was institutionalized at the London County Lunatic Asylum in Banstead. Curiously, staff found him lucid and cooperative, with no epileptic episodes, though he was prone to suicidal ideation. Dr. Shaw, a German speaker, interviewed Müller and found him intelligent, self-aware, and plausible, albeit evasive. In June 1893, Müller was declared “fully recovered” and discharged.

Returning to Berlin, Müller persuaded his estranged wife to reconcile. He appeared eager to work again and live a quiet, reformed life. But beneath this facade, he was already forming new attachments—including with Margaret Hanneman, a woman with whom he fathered a son. In 1895, after sending his legal wife away, Müller stole her inheritance of 1,600 Deutsche Mark and fled to the Netherlands with Margaret and their child. The trio lived off stolen funds, alternating between Amsterdam and Rotterdam, while Müller worked as a watchmaker.

In 1895, not long after being welcomed back into his family home, Gustav Müller sent his wife to a circus one evening and used the opportunity to steal 1,600 Deutsche Marks from her inheritance. He fled with another woman, Margaret Hanneman, and her one-year-old son—who was later revealed to be Müller’s biological child. The trio first settled in Amsterdam, then Rotterdam, living off the stolen funds while Müller resumed work as a watchmaker.

In October 1897, Müller’s mental state dramatically deteriorated. While preparing mussels for a meal, he claimed to hear a voice commanding him to kill. Acting on the impulse, he nearly decapitated Margaret by slashing her throat and then murdered his toddler son in the same manner. He mutilated the corpses by severing their ears, placed the ears in his pocket, and walked directly to the local police station.

Initially, officers thought he was either drunk or insane. But when Müller produced the bloody ears and calmly explained the crime, they realized he was telling the truth. Police Chief Strang and two officers rushed to the residence, where they found the bodies exactly as described—brutally slain in a blood-soaked room.

Under questioning, Müller confessed not only to the murder of Margaret and the child, but also claimed he had previously murdered his parents, several wives, and countless children. He even alleged he had killed thousands across the globe, though none of these additional murders were ever substantiated. His parents were later confirmed to be alive in Germany. Authorities believed Müller may have committed other crimes in British colonies, particularly in India, but lacked evidence to proceed with investigations abroad.

Following his arrest, Müller refused to eat, attempting suicide by starvation. On December 2, 1897, he was acquitted of murder by reason of insanity by the District Court of Rotterdam. He was committed to an asylum, the location of which remains unknown, and was never heard from again. He is presumed to have died in institutional care.