Fabienne Kabou, 39, went on trial for the murder of 15-month-old Adelaide which shocked the country in November 2013.
The French woman of Senegalese origin described her well-off childhood in Dakar before she moved to Paris to study philosophy and architecture and fell in love with a sculptor 30 years her senior, Michel Lafon.
"In 2011 I fell pregnant with Adelaide, she was born in August and I ended up killing her, 15 months after her birth," she told the court in the northeastern town of Saint-Omer.
Kabou travelled with her daughter from their home in Paris to the northern resort town of Berck-sur-Mer where she enquired about the local tides before heading to the beach.
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She said goodbye to her sleeping daughter and placed her near the water on a wintry night.
The baby's lifeless body was discovered early the next morning by prawn fishermen.
"Witchcraft. That is my default explanation because I have no other," she told the court.
Kabou said she had spent some 40,000 euros ($60,000) consulting various "witchdoctors and healers" before carrying out the murder.
"Nothing makes sense in this story. What interest could I have in tormenting myself, lying, killing my daughter? I spoke of sorcery and I am not joking. Even a stupid person would not do what I did."
'I had hallucinations'
Kabou's lawyer Fabienne Roy-Nansion pushed her to explain why she thought evil forces were at work.
"For many years I struggled to wake up in the morning, my feet were paralysed. I had hallucinations, like the walls which didn't stop trembling," said Kabou, who is charged with premeditated murder and faces life in prison.
From the start she has made little effort to hide or deny her crime, and video surveillance allowed police to track her down 10 days afterwards to her home - a renovated art studio where she lived with Adelaide's father.
Roy-Nansion describes Kabou as from a well-to-do Catholic background and of "remarkable intelligence".
A court-appointed psychiatrist found that her "psychological status is largely influenced by cultural references and an individual history linked to Senegalese witchcraft that radically altered her view of the world".
However a lawyer for a children's group that is a civil party to the case, Jean-Christophe Boyer, accused Kabou of using witchcraft as a defence strategy.
"You are faced with a very intelligent woman who knows she must not say she is mad, but give enough to the experts to appear mad, so you have sorcery and it is part of her culture," he said.
Another court psychiatrist, Paul Bensussan, said her act was possibly triggered by a deep depression related to the birth of her child.
Her lawyer has said the child was born in the couple's home and was never registered. No one close to the couple, not even Kabou's mother, knew of her existence.
The pregnancy "was a happy surprise for her, not necessarily for the father. I think she felt deeply alone," Roy-Nansion said before the trial.
The father, Michel Lafon, a sculptor, did not take an interest in or recognise the child, according to court documents.
A DNA test was carried out after Kabou's arrest to prove his paternity.
Kabou has told investigators she chose the town because it sounded like a "sad" place. "Even the name is sad." Berck means means "yuck" in French, though it is the Flemish word for dune.
"The two years before the murder of my daughter were the worst of my life. The two years in prison have been calmer and more peaceful," she said in court.
