If someone wrote a book saying Madeleine was dead, it wouldn't be libellous, but it could be said to affect the effort put into searching and hence cause damage to the search.
If a former coordinator writes a book, narrates a documentary and regularly appears on TV and in the written press asserting that he somehow KNOWS what actually happened... how would you feel if it were your child, niece/nephew, parent / best friend who was missing?
Particularly if the same individual clearly had only one other case of such a nature and in which the family were in jail before they could even breathe?
And with the same coordinator who, in neither case, ever found any evidence of what had actually happened to the child?
Be honest. What if someone close to you had disappeared?
ETA. Stand back. Forget all the anti/pro arguments.
Imagine that someone very close to you had disappeared without a trace. How confident would you feel that the lead investigator was trying to convince the world that you and the rest of your family / friends were involved when you were certain that they weren't and that precious time was being wasted?