But seriously ….. a more plausible path is that instructors sometimes create interruptions to ensure you know how to focus on the aircraft. My instructors would open windows at inopportune times: little did they know but it caused me to fly an aircraft with a canopy that can slide back during flight, a “convertible”. In aircraft where you can, I’ve definite heard of instructors opening doors during flight.

The plausible accident is exactly that: instructor opening a door as part of emergency training. Of course it’s much harder to explain lack of seatbelt, or how he got up from his seat

You have to be able to handle a door or window opening in flight because there can be mechanical failures where that happens. And if we’re stretching things, the student pilot panicking could cause a sudden jerk of the wheel, throwing an unrestrained passenger out. It could happen. Extremely unlikely but it could …… except the seatbelt.

Authorities initially looked at whether a mechanical issue with the aircraft may have played a role

I think they may have meant if there was a gas leak or something that might have affected his mind? Afaik there were some flight and diving accidents where that was a contributing factor.

What if it was....Murder?!?