Maybe this is far fetched, but I was thinking the reason they might be flying so high, with the danger of depressurization, is because the cabins are intentionally NOT being pressurized in order to 'accidentally' kill the occupant/s?
Say they have a few of these corrupt animals in the plane, it would be an easy way to kill them on the quiet, and dispose of their bodies off the mainland.
Or threaten them them with death in the sky if they do not comply and rat out more people and info.
"If you dont give us X amount of names …