My understanding was Lucius came home and “found” Narcissa burned in the remnants of the house, or at least remembered doing so. It just doesn’t make sense that a clever, cunning man (who brought Draco to see Death Note and criticized the plot) would find no trace of his wife and, knowing Dumbledore to be famously soft-hearted, would just unquestioningly believe that story.
My understanding was Lucius came home and “found” Narcissa burned in the remnants of the house, or at least remembered doing so. It just doesn’t make sense that a clever, cunning man (who brought Draco to see Death Note and criticized the plot) would find no trace of his wife and, knowing Dumbledore to be famously soft-hearted, would just unquestioningly believe that story.