How? Because Silverstein waved a magic wand, uttered an accompanying spell, on tv of all things "hmmmm, hwwww, o me, o my it's been such a tough day already, lets ..... lets just go ahead and pull it..... snifff.... sob...", and poof, sheeza all come a tumblin down. Meanwhile, try to ignore the NYFD personnel who were on site at Ground 0 and were later recorded attesting to the sequence of explosions that preceded the towers free-fall collapsing that, of course, may require a head examimnation to acknowledge.