Nearly two dozen executives in the arms-dealing business were in Las Vegas en route to meet a supposed defense minister from Gabon when FBI agents moved in. Twenty-one were arrested, accused of offering bribes to a foreign official.

Last week, lawyers for the defendants, and some of the executives themselves, piled into the ceremonial courtroom of the E. Barrett Prettyman Courthouse in Washington to hash out disputes about evidence and the scope of the case — the government’s most ambitious and controversial Foreign Corrupt Practices Act prosecution.