By 1916, the young Frenchman had volunteered for the French Army in the First World War. After being wounded in battle Petiot was sent to a rest home, where he was arrested and jailed for stealing army supplies and morphine. He received a second diagnosis of mental illness at this time, yet returned to the front in 1918. Not long after his redeployment, Petiot allegedly injured his own foot with a grenade. A third diagnosis of mental instability followed, leading to his discharge with a disability pension.

Petiot enrolled in an accelerated medical education program after the war. He completed his schooling in eight months, interned at a mental hospital in Evreux, and then received his medical degree in 1921. The newfound status seemed only to accelerate his life of crime; Petiot reportedly pilfered addictive narcotics for personal use and distributed them among patients. He performed illegal abortions and stole everything from a stone cross to money out of the town treasury. In 1926, Petiot struck up an affair with Louise Delaveau, the daughter of one of his patients. Delaveau vanished not long after the affair began. While Petiot was never officially implicated in the disappearance, Delaveau may have been his first victim; neighbors said they saw Petiot loading a trunk into his car around the time the girl disappeared. Related: HENRI DÉSIRÉ LANDRU: FRANCE’S SEDUCTIVE SERIAL KILLER That same year, Petiot turned his attention to politics, mounting a successful bid to become mayor of Villeneuve-sur-Yonne. Once again, he exploited his position of power for personal gain—this time by embezzling town funds. Petiot married the daughter of a wealthy local butcher in 1927. They had a son the following year. His shady civic dealings, meanwhile, were catching up to him. After multiple reports of malfeasance, Petiot was suspended and eventually resigned as mayor in 1931. Bizarrely, he still managed to secure an elected seat on the Yonne Departement council in 1932—a position that he lost just a few months later after stealing electricity from the town.

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With his political career at an end, Petiot moved to Paris. There he faked medical credentials to present himself as an accomplished doctor. The deception worked; Petiot’s reputation drew in patients, and in 1936 he was granted authority to issue death certificates. Rumors of his old scams resurfaced—illegal abortions, excessive prescriptions. Yet it was the rise of Nazi Germany and the German occupation of France in 1940 that led to Petiot’s deadly rampage and his sinister sobriquets. Related: 10 DEMENTED DOCTORS THAT WILL MAKE YOU SICK According to his own account, Petiot worked with the French Resistance during the occupation. He planted booby traps, developed weapons that could kill without leaving forensic evidence, and met with high-ranking Allied commanders. While the veracity of these claims remains largely unsubstantiated, Petiot was cited as a source many years later by Colonel John F. Grombach, the former head of the independent espionage agency known as “The Pond.”

What does seem certain is that Petiot claimed to operate a secret escape route during the occupation. Under the codename Dr. Eugene, Petiot told French Resistance fighters, Jewish refugees, and others wanted by the German government that he could assist in their escape from war-torn Europe to Argentina. For these services, he charged each escapee a fee of 25,000 francs. The proposal was a trap, of course. Petiot told his victims that they required an inoculation before entering Argentina, and used the opportunity to inject them with cyanide. He would then steal their valuables and dispose of the bodies by dumping them in the Seine, burying them in quicklime, or burning them in his fireplace. Related: 5 SUPER-TWISTED SERIAL KILLERS YOU’VE NEVER HEARD OF In March 1944, neighbors complained of a foul stench coming from Petiot’s home in Rue Le Sueur, and of noxious smoke billowing from his chimney. Authorities were summoned. When they searched the premises, they found the remains of numerous victims—including, reportedly, charred human remnants smoldering in the fireplace.

Petiot evaded capture for a short while by adopting an alias and growing out his beard. He was captured in October 1940 and held under suspicion of murder. His trial began in March 1946, by which point coverage of the case had spiraled into a media circus. Petiot maintained his innocence to the end, claiming that he had killed only “enemies of France,” German soldiers and double agents, as part of his work with the Resistance. Related: DID DR. SAM SHEPPARD MURDER HIS WIFE? Authorities, however, could not find any connection between Petiot and the French Resistance. Many of the Resistance groups Petiot named and the exploits that he claimed to have been a part of never existed. Ultimately, Marcel Petiot was found guilty of 26 counts of murder for profit. It was estimated that he netted 200 million francs from his ill-gotten gains. Many suspect he actually claimed upwards of 60 victims. On May 25, 1946, he was beheaded by guillotine.