> There are no central repositories as to the location of arbitrary banknote serial numbers.
Why do you say that?
All that's needed is banks tracking serial numbers and associated persons as cash leaves the bank and enters it. The serial numbers on American cash seem machine readable, and on each bill they are printed in two places near opposite corners - as if they are designed for automated reading.
It doesn't have to be perfect, logically infallible, alibi-proof evidence. You could build a pretty good graph of who is doing business with whom, especially by examining repetitions of the same edges. At worst, it seems useful for intelligence tasks and to obtain worthwhile leads to pursue.
Why do you say that?
All that's needed is banks tracking serial numbers and associated persons as cash leaves the bank and enters it. The serial numbers on American cash seem machine readable, and on each bill they are printed in two places near opposite corners - as if they are designed for automated reading.
It doesn't have to be perfect, logically infallible, alibi-proof evidence. You could build a pretty good graph of who is doing business with whom, especially by examining repetitions of the same edges. At worst, it seems useful for intelligence tasks and to obtain worthwhile leads to pursue.