It's so simple; anybody can figure this one out.
It goes like this, rogue elements inside the US government came up with a plan, to commit mass of their own country men. This plan was incredibly complex. They involved hundreds of people before hand and the one of the ring leaders said.
“Hey has anybody phoned Silverstien yet?"
Ring, Ring........
" Hi Larry, we've got a plan, it involves loads and loads of people and wondered if you wanted a piece of the action"
" Really? ,what’s going on?"
" Well without going into too much detail, maybe you should plant loads of explosives inside WTC 7 and get better insurance on it"
" Em, interesting, it's sounds a bit dodgy, maybe I should phone the authorities"
" Oh it's ok, they are involved also"
Pause.
“Ok I'm in, it sounds perfect"