Sevarius’s briefcase was where Anton Sevarius kept his notes.
When Goliath abducted Sevarius from Gen-U-Tech, Sevarius dropped his briefcase. It was found by Elisa moments later. She evidently turned it over to the Gen-U-Tech security guard, because Owen later mentioned to Xanatos that it had been found.
Sevarius’s briefcase was gray and monogrammed, except his name was spelled wrong as “Servarius.” “(The Cage)”