This looks like a lynch mob.
Until we know more, please give the FO the benefit of a doubt.
Based on facts from Mr BEA and a prosecutor we know that
- FO changed his demeanor towards Capt during landing brief.
- Capt left the cockpit for some reason after that.
- Cockpit door was locked from inside.
- Breathing sounds are heard in the cockpit but no attempt to comms with ATC and no reactions/improper reactions to the immediate surroundings.
This could all be indicative of so called subtle incapacitation. It may have started with the change in attitude during the briefing. If Capt didn't notice this and went to the loo instead, it could have gotten worse until FO was unconcious or incapable of coherent thoughts - a hypoxia like state of mind.
Such things has happened before. Hypoxic pilots knows to descend if they recognise hypoxia. If there are other problems not related to hypoxia this won't help. Brain aneurysm? Heart infection (TWAR)? Blood clot/deep vein thrombosis?
Subtle incapacitation was one of the reasonings behind the Staines crash.