Yes, if there was a second change of heading that pretty much negates the hypoxia theory - although depressurisation could still have been used as a weapon to incapacitate everyone else. Hijacking is far fetched, the logistics are too great and the risk of failure too high. So if there was a change of course, odds on it was towards deeper water. No change in heading and hypoxia is back as number one suspect. In the absence of confirmation, the lack of transponder signal still increases the odds that this was a deliberate act. Inmarsat or whoever it is that has the logs must have about 10 pings. That will allow calculation of direction and speed and hence any navigational changes. Even if there was no change in HDG murderous intentions are not completely ruled out, as any culprit might prefer self induced hypoxia to violent concussion. In every investigation like this innocent people who may have crossed the scene will be looked at. There can be no squeamishness about doing this.