we heard about detieration, reinforcing rusting and the concrete. that should be looked into. could have been a factor. had there been alterations to the building overtime. was there a load on the structure recently or at the time of the fill you're? we don't know that. >> what about gas? >> gas -- an explosion with gas? >> yeah. could that have -- >> it's happened in other structures. in fact, it happened in a very famous progressive collapse like this. in 1968, a structure in london, there was a gas explosion that cau caused a progressive collapse like this. >> the reason i'm asking, you see right through the middle.