Now, now- no-one said it went missing in one year.
Let's do the maths assuming its been going on for a longer period, shall we?
Let's assume that this massive conspiracy started in 1947, because... hey, Roswell's been blamed for every other conspiracy so why not 9/11 as well?
That would mean that, on average, this secret society misappropriated about $60Bn a year. (NASA gets an average of $9ishBn and gets bitched at for it.- and the Black Ops budget was only about $50Bn last year...)
Now a powerful group of people in charge of a few multinationals working together? I can buy that as a conspiracy. You don't get to the top by being nice. Corrupt senators- even corrupt Presidents? Yeah, I can buy that too- they're only human. Aliens? That's another issue entirely unless ET is flying a 767 nowadays.
Even that someone like the US military could be bribed/conned out of that amount of money- so it'd be recorded as flowing to (say) BAE, Lockheed or Boeing but with nothing to show for it- would be believable. You'd want heads to roll, but it'd just go down as "oh, the public sector/military procurement/etc fucked up again. What a surprise."
But $2.3Tn going MISSING (which, I imagine, is what "unaccounted for") means? As in someone siphoned off enough money to cover the national debt of the UK? Not a chance. Even the $60Bn average over 50-ish years wouldn't exactly go unnoticed.
Anyway- short of building a secret fleet of AT-ATs and a Death Star (in orbit around Jupiter), what would they use $2.3Tn for?! The War on Terror has only cost about half of that and that's been an intensive bunch of wars for almost 10 years. For $2.3Tn they could have dropped that much ordnance on Afghanistan/Iraq/Pakistan that Bin Laden could have been declared 'missing, presumed utterly pulverised'.
Of course, I could be a government pawn writing this from the wonderful solid-gold office block the Government secretly launched into orbit with a small fraction of that $2.3Tn.