They did not.
They knew what the evidence suggested.
They knew what was physically possible.
They knew human bone had been burned.
They knew women had vanished.
They knew Landru possessed their belongings.
But Landru never gave them the final sequence.
The Chimney
Then the neighbors' memories became evidence.
That smoke.
Those smells.
Things once dismissed as strange behavior now looked sinister.
Witnesses remembered the chimney producing offensive odors.
Some described the smell as deeply unpleasant.
A butcher reportedly told investigators it resembled burning flesh.
Smoke had risen at odd times.
The country house had seemed to consume an unusual amount of fuel.
Landru had purchased substantial quantities of coal.
At the time, none of that was enough to call police.
After human bone fragments were recovered from the ashes, it became part of a pattern.
Landru's greatest advantage had been that every suspicious detail looked innocent on its own.
A woman takes a train.
Normal.
A widow remarries.
Normal.
A fiancé sells furniture.
Possible.
A house burns coal.
Normal.
A chimney smokes.
Normal.
A man uses a different name.
Suspicious, but criminals and fugitives often did.
Put together, the same details became something else.
A system.
What Happened Inside?
The most haunting question remains the one investigators could never fully answer.
How did Landru kill them?
Poison?
Strangulation?
Another method?
The prosecution considered possibilities.
But no surviving eyewitness could say.
The bodies were too thoroughly destroyed.
Forensic medicine could prove human remains had been burned.
It could not establish the precise cause of death for the missing eleven.
That weakness sounds enormous.
In a modern courtroom, the absence of cause of death for nearly every alleged victim would invite fierce attack.
It did in 1921 too.
Landru insisted that the women were merely missing.
If police had failed to find them, that was the police's problem.
Why should he explain the private lives of adult women?
Perhaps they had left.
Perhaps they were somewhere else.
Perhaps they did not wish to contact their families.
He repeatedly treated the prosecution's inability to find them as evidence of the prosecution's incompetence.
The silence of the dead became his defense.
283 Women
Meanwhile, investigators were decoding the larger network.
Landru's records showed contact with around 283 women.
That number horrified the press.
Were there hundreds of victims?
There was no evidence for such a conclusion.
Most of the women were traced.
Many were alive.
Some had rejected Landru.
Some had been rejected by him.
Some had lost money.
Some relationships had ended.
That process actually strengthened the murder case.
Investigators could compare the women who survived with the women who disappeared.
Among hundreds of contacts, a very specific group vanished after becoming deeply entangled with Landru.
The missing were not randomly scattered throughout his correspondence.
They clustered around circumstances involving money, travel and the isolated properties.
It became increasingly difficult to explain eleven disappearances as coincidence.
The Selection Process
Landru's notes revealed something coldly practical.
He cared about money.
A woman's finances mattered.
Her relatives mattered.
Her independence mattered.
A woman with little money offered limited opportunity.
A woman closely watched by sons, sisters or friends posed more risk.
A woman with savings and few people monitoring her could be far more attractive.
The romantic correspondence hid financial due diligence.
He learned where they banked.
What property they had.
What income they received.
What furniture could be sold.
Which securities they owned.
Sometimes he acquired powers of attorney.
In effect, he turned courtship into asset acquisition.
First emotional access.
Then financial access.
Then physical isolation.
Then disappearance.
Then liquidation.
After the Disappearance
This was another powerful part of the circumstantial case.
Landru did not simply lose contact with women.
After certain disappearances, he acted as though their property was available to him.
Furniture moved.
Possessions appeared in storage.
Jewelry changed hands.
Financial assets were manipulated.
If the women had independently gone somewhere else, why did the man they left behind benefit?
Landru had explanations for almost everything.
That was his talent.
But each explanation had to survive next to ten others.
One woman voluntarily gives him her belongings.
Possible.
Two?
Possible.
Three?
Perhaps.
Ten women independently abandon their property, cease all family contact and disappear after associating with the same man?
The probability begins collapsing.
The War as Camouflage
The First World War was not just background.
It was part of Landru's method.
Without the war, his pattern might have been detected sooner.
But France from 1914 to 1918 was a nation of disrupted communication.
Families did not always know where relatives were.
People relocated.
Records lagged.
Soldiers vanished in battle.
Widows moved.
Economic hardship forced sudden decisions.
Police resources were stretched.
Landru himself was a fugitive already using false identities.
Against that chaos, one lonely widow ceasing correspondence did not immediately look like murder.
War gave him noise.
He operated inside it.
And the women he targeted were partly products of that same war.
The absence of men at home created loneliness.
Death created widows.
Economic uncertainty made promises of security attractive.
The war created the audience for his advertisements.
Landru turned a national catastrophe into a private hunting ground.
Two Letters That Broke the Pattern
And yet the entire structure began collapsing because two families refused to accept silence.
That is one of the most remarkable features of the case.
Not forensic science.
Not a confession.
Not a body discovered by accident.
Questions.
Where is my sister?
Who is this man?
Why does the name not match the property record?
Why has another family asked almost the same thing?
The mayor of Gambais noticed repetition.
Repetition is the enemy of a serial offender.
A single unusual event can be explained away.
Two nearly identical events demand comparison.
Once Célestine Buisson and Anne Collomb became part of the same inquiry, Landru's aliases began working against him.
Every false name gave police another connection to trace.
The Black Notebook
The notebook made the case even stranger.
Most criminals try to remove records connecting themselves to victims.
Landru catalogued them.
The notebook was not a confession.
It did not say:
I killed this woman on this date.
Instead, it provided something almost as useful.
Structure.
Police could use it to ask:
Who is this?
When did he meet her?
When was she last seen?
Which alias was he using?
Which train did he take?
What financial operation followed?
Which personal possessions later appeared in his storage?
The notebook allowed investigators to reconstruct a criminal timeline from fragments.
It was less a diary of murder than a ledger of opportunity.
And Landru's bureaucratic precision became a witness against him.
Eleven Names
The eleven alleged victims eventually stood at the center of the prosecution.