That's an amazing assertion with nothing to support it and everything to contradict it but you're doing the ignoring thing...
Suicide bomber sets off his bomb, bomb does no structural damage (they really can't you know), but kills a lot of people. Some people would have been wounded, typically shrapnel wounds and in offices that had relatively soft partitions you'd get a lot of survivors, look at ANY suicide blast in Israel that was targeted on civilian targets, more wounded than dead. They might have set themselves off in the lifts i suppose, but how to time it, there was no tight coordination of timing shown in the attacks, hell attempting it would be the work of rank amateurs and idiots. Or perhaps in another more secluded area, which raises the question of why on earth they'd bother. Either way the idea that they set themselves off and did not leave witnesses is incredible.
Then there's the "what the fuck was that" factor. Hundreds of firemen in addition to other people in the building will have been scouring the place for people trapped. It's possible that they found the remains of an office full of people spread over the furniture and not reported it, but it's incredibly unlikely. Not one person going forward saying "i was in the basement and someone exploded!"
Perhaps it was an attack on the building's structure! But since they'd tried that with a sodding van full of explosives and failed you'd think they might have caught on that it wasn't going to work. Not to mention of the inconsistent points at which these explosions came from, to destroy a structure you take out the supports in an organised manner, not at random, buildings are designed for an element of load distribution that would negate the effect. Even if they were stupid enough to try it there's also no witnesses to this attack, no one going past the main structural elements noticed the new red decor?
Your mind is open but empty. Although your version of open is rather, selective, by the looks of things.