The info coming out says that the cockpit was locked when the pilot left. When he returned, he punched in the code to be readmitted. The copilot them hit the lock button to prevent the door from opening. That button will lock the cockpit for an additional five minutes each time it is pushed. No indication of any distress from the copilot who was breathing normally.
Deliberate act wihtout question.
Well, then it’s Mass murder. Now for the reasoning.