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
M. Robin may well have a public duty to report the facts but the above is subjective speculation on his part. It is not for him to comment on what may or may not be the "most plausible" explanation - at this stage this can only be based on what little evidence he knows now. He says the action of reducing the altitude can be "analysed" as an intention to destroy the aircraft - but it could equally well be "analysed" as an intention to get the aircraft down quickly (e.g. cockpit fire and many other scenarios that could leave no CVR trace). It's possible he wound the altitude down to 100 ft (the lowest it will go) initially when initiating an emergency descent thinking he would adjust it later, and for whatever reason he got distracted or was unable to adjust it because of subsequent events such as choking on smoke/heart attack/stroke.
The point is that there is no such thing as "reasonable doubt" when you are talking about a one in several million flights possibility. If he did indeed kill 149 people deliberately, then that would be an incredibly rare event in aviation history. If you are considering it as such, then you have to consider other very unlikely scenarios as possibilities if you are doing your job properly as an investigator, otherwise there can be no credibility to the process.