Originally Posted by mseyfang
I think it is important to differentiate between what is established fact and what is theory
Precisely. However based on possible outcomes of unknowns, certain outcomes can be eliminated, and likelihoods can be assigned to others:
Facts
(assuming being reported by authorities
as fact is true - only the transponder timing is verifiable from an independent source)
ACARS stopped transmitting at 01:07
Last voice communications 01:20
Transponder ceased transmitting 01:22
Assumpton A: ACARS switched off deliberately
It was either a member of the real crew communicating 'roger that' - in which case whatever happened is most likely deliberate crew action,
OR
It was not a crew member communicating, indicating that at that time already someone other than the crew was in control of the aircraft, for purposes unknown
Assumpton B: ACARS disconnected due to some malfunction
13 minutes later crew were either not aware of it, or whatever was the case did not trigger enough alarm to notify ATC of a problem
2 minutes later issue propagated to a transponder failure.
Beyond that, crew were either too busy to communicate, or failure propagated to comms systems, or crew became incapacitated (or all of these in some sequence). In this case a good explanation needs to be found on how the aircraft could have stayed in the air and conducted the observed flight path for several more hours.
Likely conclusion
I don't have the technical knowledge to go through all possible failure paths in Assumption B, but I'm sure many have worked overtime in Seattle to do so, and my assumption is that most possible failure scenarios have either been eliminated, or tagged as extremely unlikely requiring the line-up of too many layers in the swiss cheese to make it a plausible one.
The logical conclusion is then that it must have been Assumption A, either initiated by the crew (wilfully or under duress) or by a yet unidentified third party. It is this scenario that is being communicated at present in a rather assertive way.
Quite possibly the last ACARS transmission had some information whether it was deliberately switched off, which would actually make Assumpton A. a fact.