Their method:
"In order to obtain the case, the conspirators exploited a loophole in Citi's account security protocols, which caused Citi's account reconciliation systems to treat identical, near-simultaneous withdrawals as duplicates of a single withdrawal from an individual Citi Checking account," prosecutors alleged in the indictment. "In exploiting this loophole, the conspirators withdrew identical sums of money in succession from a single Citi checking account all within a specific time window. This allowed the conspirators to fraudulently withdraw several times the amount of money deposited into each account."
