Noir Desir frontman Cantat was convicted of beating his actress girlfriend Marie Trintignant to death in a Vilnius hotel in 2003. A Lithuanian court jailed him for eight years, and he was released on parole in 2007.
The couple's two children, a 12-year-old boy and seven-year-old girl, were not present in the house when Rady committed suicide, but one of them made the chilling discovery when returning home around midday Sunday, officials said.
The 45-year-old singer was questioned by police in Bordeaux late Sunday but no action was taken against him.
Cantat has been free on parole since October 2007.
Known for his edgy music and dark lyrics, Cantat had married Rady, of Hungarian origin, in 1997 but they separated soon after their daughter's birth when he met Trintignant.
Rady was a writer and theatre actress who had translated works into Hungarian, including Marjane Satrapi's award-winning animated works "Persepolis".
She had spoken out in defence of her ex-husband during his trial in Lithuania, saying he had never been violent with her during their marriage.
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