just because they have job you look down on does not mean they are not smart. also they could care less if it was ever found. even if the plane was found the day of the crash it still covers up the theft if they timed the crash over the ocean.
Bottom line is that the simplest answer is usually the correct answer. This was done by someone who had direct control over the aircraft. Most likely one of the pilots. Or it was mechanical. How baggage handlers would be able to make a plane go off-course, cut communications, and fool the best investigators on the planet for a year is a bit of a stretch for me.