It’s not lost, it’s just a illegal appropriations. The money was purposefully steered towards illicit foreign aide, greasing palms, and some to probably to acorn type organizations and I’m sure a few bucks made it into Campaign coffers and young grand daughters of politicians.
It’s been purposefully obfuscated. The U.S government has been in business for 200+ years. Accounting is as old as well as old as the oldest profession.
Nobody loses or misplaces 6 billion dollars.
Want to see the money - go the Management Officer at every mission abroad and look at the budgets. It requires a contract officer and a certifying officer to spend any funds. The Management Officers, is slick will appoint others to serve as alternate or backup certifying officers/contracting officers and use those they rate professionally to spend the money or obligate it. However, the management officer is still on the hook if only because he is where the buck stops and he reviews all spending at post.