If it was terrorism, I don't see why depressurizing the aircraft would be necessary once they gained access to the cockpit. Killing everyone on an airliner would surely be secondary to the bigger goal of using it as a Kamikaze weapon, 9-11 style. OTOH it has occurred to me that sabotage by a disgruntled employee, eg mechanic or ex-mechanic, could theoretically be possible... but would be fairly complex to pull off in an aircraft like a 733.
If one pilot was in the lav while the other was not (contrary to the rules) wearing his mask and fumbled with the mask.... that could have been enough to do it after the initial event. What was strange (and would seem to negate the possibility of any pilot being in the lav) is that they seemed to have some sort of pressurization problems and had enough time to report that but not descend to 10,000... unless the CA was foolish rnough to send the FO in the back.
It all depends on the aircraft. If there was the cockpit access system with the video monitor, and the unlock mechanism, then one pilot could have left the cockpit legally. And wearing your oxygen mask while the other pilot is gone is an FAA reg, not JAR OPS. The fact that they had called and reported a problem seems to suggest that there was in fact a problem with the pneumatics/pressurization, and they handled it completely wrong. You are completely right that the first thing that should have been done was to get on oxygen, and seriously think about decending. It will be interesting to see what the investigation discovers. Either way, it is a horrible tragedy, and a shame.
Maybe not at 34,000 feet, but evidently they hit a mountain and I can't think of too many mountains that are at 34,000 feet. After he created the text message it may have just kept trying to send, and as they came close to impact it got within enough range of a cell to go out.
What I find VERY ODD is that last comment about the bodies, "None of them seem to have their oxygen masks on." Only the F/O had his mask on and was STILL passed out?
I'm no rocket scientist, but if the masks came down I'd at least put the thing on. Wonder if there really was something wrong with ALL the O2 on the aircraft (sabotage)...