you are completely and utterly wrong.
The Code Penal and the Code Civil in France requires that a procedure be opened when a loss of life occurs. It is called "instruction judiciaire".
The BEA carry out their investigations entirely independently.
If a plane went down with only the pilot on board,, no damage or loss of life on the ground, BEA would investigate on the one hand and an "instruction" would be opened at the same time. It has happened countless times. The purpose is to establish the cause of the death(s).
Under some different systems, a coroner would carry out the same function
A Procureur has a duty like any public servant, to be open and inform the public of what is known.
Do not be confused into thinking that the intervention of a Procureur means that criminal actions are considered or envisaged or even contemplated. It is simply a matter of procedure according to the laws of France. When you are better informed about the "speciality" of the role of a Procureur we could hold a further conversation.
The most plausible and probable interpretation for us is that the co-pilot, by a voluntary abstention, by voluntary abstention, refused to open the door to the cockpit to the flight captain and activated the button to start descent. So he activated this button to initiate loss of altitude for a reason that we are completely unaware of today but that can be analyzed as an intention to destroy the aircraft.
The niceties of the french legal system notwithstanding, this chap looks like he's already made his mind up about the incident. You can appreciate why one might be confused, n'est-ce que pas?