By Reid Barton.
Each of the eight puzzle headers in Washington contains a three-by-three "access keypad" with some buttons illuminated, and two rows of four small red LEDs with one light on. Place the eight 3x3 grids in two rows of four, with the placement of each grid indicated by which of the eight red LEDs is illuminated. This gives you two 3x12 grids of buttons, with some buttons illuminated. These can be re-parsed into six Braille characters each; read that way, they spell GADGET and MOSCOW. So the fourth agent is Inspector Gadget, and he is located in Moscow.