I'm quite convinced that there was no fireball. History is littered with examples of people seeing flames when they never did. In fact, a rig worker claimed to have seen a fireball in the sky when MH370 went missing when in fact the plane was hundred of miles away. When the track of the jet proved it was nowhere near, the fireball sightings were quickly forgotten.
The video I have seen is clearly space junk burning up.
My thoughts go out to those involved. Whilst it's easy to jump to the terrorism or deliberate crashing, recent history shows that several fully serviceable planes (both Airbus and Boeing before anyone goes down that route) have come to harm due to handling issues.
Meanwhile 12 hours in and there's still no sign of it. Not acceptable in 2016!