Assume for a minute:

1. A Hijacking / suicide mission was well planned / executed.

2. It was a test .

3. No claim of responsibility would be made.

4. The airplane should be difficult if not impossible to find.

5. The cause and methods used would be near impossible to detect.

6. If undetected, the cause and methods could be used again.

Think lethal chemical or gas release in the cabin while wearing a protective mask. Then fly to remote location (end of fuel).