[devane617]

>>...However this does not explain the depressurization...<<

Unless of course the pilot depressurized the plane for a reason. I assume that can be done in a manual way by the pilot. As a last ditch response to a critical situation the pilot may have actually pulled the plug.

[Kelly_2000]

"Unless of course the pilot depressurized the plane for a reason. I assume that can be done in a manual way by the pilot."

Hmm nice theory, that would fit, the plane fills with toxic fumes from the AC, the pilot attempts to vent the gasses by depressurizing the plane.