[Brett66]

An ICBM could get the velocity to do it, but it doesn't have the targeting capability. There's really nothing, except experimental SDI technology that could do it, definitely not within a terrorists capability.

[Tall_Texan]

There's no chance it could be external terrorism (an external weapon striking the craft). As for internal terrorism (some form of sabotage to the craft), who would plan something that would cause the destruction of the craft on re-entry when it would be so much easier to plan something that would cause destruction at lift-off?

At this point, I have no reason not to suspect failure of the heat shield. I frankly doubt there will be much left of the craft with which to peace together what happened in any definitive way.

But two things I'll safely predict. First, a good many items of junk will be reported as fallen Columbia debris. Second, within a week somebody on E-Bay will try offering that junk as "Space Shuttle Debris".

[babygene]

Although the Islamic’s do not have a such a missile (note that they didn't need one for the WTC), Sabotage is certainly within there capability...