First appearing in Dark Mirror and then Logan's Shadow, the Hidden Evidence is a mixture of classified folders, hidden bodies, lockers and other clues, which contribute to Locked Files when acquired. These Locked Files are a combination of Concept Art, Audio Files and Bonus Movies, which include special 'behind - the - scenes' videos, work in progress, and animatics. Hidden Evidence also shows up in a player's inventory list, with a brief description to transcribe the history of the Hidden Evidence.
Making its very first appearance in The Omega Strain, this is a compilation of paperwork and media files pertaining to various mission, with six categories - News Reports, Mission Data, Agency Files, Political Data, Conspiracy Files and Media Files. It serves to explain and elaborate on the happenings of the trilogy - Syphon Filter 1, 2 and 3. Furthermore, when players complete special objectives, a document will sometimes appear in the inventory list. This document will later be unlocked and viewable in the Zeus Files. Zeus Files which have yet to be unlocked show up as orange - yellow envelopes with a CLASSIFIED stamp labelled on it. This classified is also present in multiple foreign languages. On some occassions, if the player collects a recorder, a black box, a laptop, a video tape or any other electronic device, the accompanying Zeus File would not be unlocked in the paperwork section but in the media files instead.