As the story goes Rumsfeld made this announcement on 9/10/2001 only to have the news of trillions of missing dollars drowned out by the events of the following day. By extension then, the attack was deliberately planned by the inside jobbers to hit the precise spot on the Pentagon where the accountants worked and the records were kept.
As usual however this is just another case of Truther reality distortion by taking quotes completely out of context to infer a meaning that is completely different than intended. Here is what Donald Rumsfeld actually said on 9/10/2001:
" In this building, despite this era of scarce resources taxed by mounting threats, money disappears into duplicative duties and bloated bureaucracy—not because of greed, but gridlock. Innovation is stifled—not by ill intent but by institutional inertia.
Just as we must transform America's military capability to meet changing threats, we must transform the way the Department works and what it works on...
...The technology revolution has transformed organizations across the private sector, but not ours, not fully, not yet. We are, as they say, tangled in our anchor chain. Our financial systems are decades old. According to some estimates, we cannot track $2.3 trillion in transactions. We cannot share information from floor to floor in this building because it's stored on dozens of technological systems that are inaccessible or incompatible.
We maintain 20 to 25 percent more base infrastructure than we need to support our forces, at an annual waste to taxpayers of some $3 billion to $4 billion. Fully half of our resources go to infrastructure and overhead, and in addition to draining resources from warfighting, these costly and outdated systems, procedures and programs stifle innovation as well. A new idea must often survive the gauntlet of some 17 levels of bureaucracy to make it from a line officer's to my desk. I have too much respect for a line officer to believe that we need 17 layers between us....
[plenty more here, please go read the whole thing]
So in other words, $2.3 trillion didn't just "go missing" (inferring it was stolen) but rather how it was spent can not be tracked by archaic, obsolete and incompatible Pentagon accounting systems.