There's a fairly obvious argument here: 1) It seems pretty clear the plane took hours to crash 2) If the cabin was full of healthy, alive passengers, they cou

There's a fairly obvious argument here: 1) It seems pretty clear the plane took hours to crash 2) If the cabin was full of healthy, alive passengers, they could have done something during that time. (It's not a certainty, but it certainly seems plausible. Armored cockpit doors aren't meant to withstand dozens of super motivated people, including cabin crew, with literally hours of time on their hands.) 3) Apparently nothing was done, so apparently it wasn't full of healthy, alive passengers. 4) Although a number of things could have killed or incapacitated the passengers in the cabin, depressurisation is fast, reliable, under the control of the pilot, and doesn't require any elaborate assumptions about third parties or deus ex machina. There are other possibilities that have been discussed elsewhere (poisoned food, perhaps), but Occam's razor suggests depressurisation. I think that's what the author was getting at with the "circumstances suggest". Given what is known about the plane, depressurisation is the most logical explanation for one of the mysteries.