I can also remember some report of an Airline Captain on his last flight before retirement loosing the plot and barrel rolling an Airline full of PAX.
You cannot discount crew loosing the plot and committing suicide deciding to take the whole ship with them.
Respected Family Men have lost the plot and wiped out their whole family wife and kids.
If its one nutcase Pax then if the crew are lax on securing the Cockpit while using the WC etc then it is feasible that a Pax pushed in locked the door killed the crew and did his wicked deeds.
As stated I cannot see organised terrorism behind this because of a lack of claims for the Evil deed.
Organised terrorism need the publicity and coverage to promote their cause and to date there have been no serious claims to carrying out such an act.
I still bar the crew or errant Pax lean towards a massive decompression with emergency descent minus the A/P
Pace