This is Whalid Shoebat’s take. He’s ex-Muslim ex-PLO I believe.
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I think an incendiary device in the cockpit could meet all of the forensic comparisons based on what we know today. A non-metallic bundle of road flares, for example. Either in the forward cockpit lav or in the cockpit itself.
Flares in the lav would have the lav smoke code coming first, not the cockpit window heat alarms. In the cockpit would have the multiple cockpit smoke sensors (several of which are deliberately *not* accessible by the crew in flight) sending error codes first.
Neither of these cases fits the ACARS code timeline. The heat sensors go off on *the other side of the plane* from the lav prior to the lav smoke alarm - significantly before. Likewise, none of the cockpit or cabin smoke sensors set off alarms - and they’re set pretty sensitive. Old line captains that still smoke and ignore rules against smoking find that lighting a *match* in the cockpit sets off the ACARS message ‘COCKPIT SMOKE’. They don’t even get to light their cigar.