Yes. Another avenue is the “plane geek” pilot had a flight simulator in his home. That means he could have tested nefarious scenarios at home without anyone knowing. I think the pilot is the key, not his horny co-pilot. The possibilities range from simple theft ... to jihad hijacking of some kind.
I thought the same thing this morning. The ‘aviation geek’ had an exact mockup to test various electronic/aviation scenarios without anyone else being aware of his doing so.