That same year, one of Petiot's patients - a Madame Debauve - was robbed and murdered in her home. Gossip blamed the doctor, but his chief accuser another patient - was soon silenced by sudden death. A woman who accused Petiot of actively encouraging her daughter's drug addiction disappeared without a trace, but things were getting hot in Villanueve, and the good doctor struck off in search of a friendlier climate.

In Paris, he was convicted of shoplifting, discharged on the condition that he seek psychiatric therapy. As World War II began, Petiot was convicted of drug trafficking, alleged to be an addict himself, but the court released him after payment of a small fine. By early 1941, with Nazi occupation troops controlling France, he had devised a get rich scheme that mirrored elements of Hitler's "final solution to the Jewish question."

Petiot bought a house on Rue Lesueur, in Paris, contracting for special modifications that were completed in September 1941. The revisions included raising garden walls, to block his neighbors' view, and construction of a triangular, windowless death chamber inside the house. As the war dragged on, Petiot made a fortune by posing as a member of the French resistance movement, offering to help Jews and other fugitives flee the country. Clients arrived at his house after dark, receiving an injection to guard against "foreign disease," and Petiot then led them to the chamber, watching their death throes through a hatch in one wall. Arrested by Gestapo agents in May 1943, on suspicion of aiding escapees, Petiot was released seven months later, when the Nazis recognized a kindred spirit.

On March 11, 1944, neighbors complained of rancid smoke pouring from Petiot's chimney, and police found the chimney on fire, with no one at home. Firemen broke into the house and found 27 corpses in the basement, most in various stages of dismemberment. Held on suspicion of murder, Petiot was released after telling police that the dead men were Nazis, executed by the French resistance.

The doctor dropped out of sight in August 1944, when Paris was liberated, but two months later he fired off a letter to the press, claiming the Gestapo had tried to frame him by dumping corpses at his home. The renewed investigation climaxed with Petiot's arrest on November 2, 1944, and while his rap sheet had mysteriously disappeared in Villeneuve, authorities had ample evidence in hand. Charged with 27 murders, Petiot admitted 63 killings at his trial, in March 1946, describing various homicides as the patriotic acts of a resistance fighter. The total may well have been higher, as one of Petiot's statements referred to 150 "liquidations," and 86 dissected bodies were pulled from the Seine, between 1941 and '43. Finally convicted of 26 counts, Petiot was guillotined on May 26, 1946.