The shuttle broke up much lower than 200K feet. Who knows what happened. After 911 terrorism can never be ruled out
You are right about the heat tiles breaking off in flight. Its normal for a few of them to come off upon re-entry. I dont think flying tiles caused the tragedy.
One thing I do know is that security at NASA uses contracted (rent a cop) security. Contracted security is much worse than in-house, and they will hire questionable people. It wouldnt be too hard for a terrorist to compromise security and put something on the shuttle, for detonation at a later time.
RWK
One thing I do know is that security at NASA uses contracted (rent a cop) security. I don't know what they do now, but my dad took me into JSC one night (they were preparing for the re-entry of one of the Apollo missions) and they had what appeared to be Air Force guards at the gates. Armed too - and they were stopping cars and checking ID. That was quite a while back though.
I distinctly remember it because even though I was just a kid we'd gone in and out of Army and Air Force bases for years and never stopped at the gate unless we needed directions. I remember thinking NASA must be a pretty important place - more important than an AF base, anyway.