I was all about the "coincidence" until they found the other two... now I'm leaning toward... well, the other way.
That's exactly my thoughts. The first two seemed like it was just someone trying to get somewhere without the proper paperwork and with Thailand having such a black-market for these things, whatever. But adding the FBI into the mix and having two more show up, and having all of these conflicting reports on what really happened then something seriously went wrong.
I don't really want to jump and say it's terrorism because it still may be just a mechanical failure but the over/under on terrorism went up a bit. Only reason I'm still skeptical on that though is because of the turn around. If they were in fact turning around due to communication failure, they could have been trying to land back at the original airport since they were only ~40 minutes out.
Another theory, the turn around was the cause of a catastrophic failure.