Nazi-occupied Paris was a terrible place to be in the waning days of World War II, with Jews, Resistance fighters and ordinary citizens all hoping to escape. Disappearances became so common they often weren't followed up.
And one man used the lawlessness for his own terrible purposes, killing perhaps as many as 150 people.
Yet it wasn't until thick black smoke seeped into buildings in a fashionable part of the city that firefighters and police were called to an elegant townhouse where they found body parts scattered around -- setting off a manhunt that led them, eventually, to Marcel Petiot.
The crime was very much of its time, said David King, who chronicled the hunt for Petiot in "Death in the City of Light."
"Paris was not a good place to be. A lot of people were trying to leave Paris, a lot of people just disappearing. He had it plotted out, a very devious plan," said King, in a telephone interview.
"Respect for the law was tarnished under the Nazis. Even if you suspected something, a lot of people were very, very reluctant to go forward, especially if they were Jewish."
Petiot, as it turned out, was a respected physician who turned serial killer by night, preying largely on Jews desperate to leave Paris by luring them in with promises of escape. He was accused of murdering "only" some 27, but authorities suspected his real toll was far higher.
King, a former history professor, first stumbled across reference to the killings while browsing in a bookstore and picking up a World War Two memoir by a spy. At first, he couldn't believe what he read.
But the grisly details stuck with him, and after he confirmed the story was true, he finished his other projects and came back to it.
"Here's a guy -- Marcel Petiot, who was accused of all the murders. Obviously very intelligent, charismatic, has a respected position, is into collecting antiques, interested in the arts," he said.
"And yet, you get to the other side, when he's accused of some of the most disturbing things you can think of: savagely dismembering bodies."
Through years of research, including perusal of Parisian police archives closed since the crimes took place, King pieced together the story of how Petiot claimed to be a member of the resistance and lured many of his victims in by promising them safe passage to South America in return for payment.
Once in Petiot's hands, the victims were told to write letters to their relatives, telling them that they were fine and would return once times had settled down. Then they were killed, most likely by lethal gas, and dismembered or burned.
"It's a microcosm of the whole Nazi terror and Paris being a bad place to be. There's got to be more than just exploiting peoples' hopes and dreams and desperation, but that's what he does," King said.
Though Petiot eluded police on at least one occasion, after appearing amid the crowd that gathered after the initial grisly discovery and speaking with a patrolman before riding off on his bicycle, he was eventually captured, tried and executed.
King, the author of several other books, said this one was particularly hard to immerse himself in due to the content, however horrifically fascinating the story.
It also had an impact on him personally.
"I'm generally a pretty outgoing person, but I'm probably a little bit more reluctant about things now," he said.
"Dr. Petiot seemed like the nicest guy -- charming, intelligent, friendly. You could just strike up a conversation with somebody like this ... I found myself on my guard more."