Hello,
During the initial news conference a NASA official commented that the foam insulation appeared to disintegrate upon impacting Columbia's left wing, i.e. the "poof" you can see on the film.
I'm skeptical of this being the cause, I think somehow a few tiles came loose and then the problem continued with more and more tiles flying off. I admit it is a strange coincidence that this area is where the problems appeared to start - time will tell.
Too bad they couldn't look under/inspect the wing during the mission. Look for this to be changed, i.e. the capability to inspect the majority of the exterior of a craft. Even if they couldn't repair the tiles, something? could have been done.
The image of a charred astronauts helmet lying in someones front yard is going to stick with me for a long, long, time.
May they rest in peace.
VINCE