Well it's a ridiculous system then as in effect the French prosecutor is passing a subjective judgment as to whether a crime has been committed not even a week after the crash, and whether a crime has or not been committed cannot be determined until the full "proper" aircraft investigation has been completed. So his subjective "gut feeling" will either be right or wrong and so many hares may have been set running unnecessarily. How can such a daft system be justified when in many cases the prosecutor will be wrong?
It is the prosecutor's job to launch an accusation if he thinks there is some data making this possible ! It is a lawyer's job to argue that this data isn't convincing.
A trial will decide. Saying such a process is ridiculous seems to me... rather strange (I wouldn't like to say ridiculous, because I suppose things are working differently in other countries ; please do not fall in this US tendency saying that "if you don't do things like we do, it means you haven't still found the right way").