I remember one of the main news stories was the 'L'Affaire Gregory'
where a young boy was abducted and killed in a village, from what I remember in the initial stages, the boy's uncle was the prime suspect, however he was released due to insufficient evidence
In the days after he was released the victim's father went to his home and murdered the uncle
then eventually, I believe the mother was thought of as a suspect
to the best of my knowledge , this case is still unresolved, but I could be wrong
In USA, the equivalent case would be the Joanbenet Ramsey case, where a child was murdered and at some point the parents were suspected and that case is also still unresolved