After the smoke question mark, there is a question mark ahead. Look to your right and move to the cave there. The hidden evidence is inside.
At the question mark where it explains the barbed wire as diamond shape boxes, go to your left. There is a place to climb up. Climb and move up. Hidden evidence is in a cave, near the skybox question mark.
At the question mark asking you to detonate the bridge, DO NOT detonate! Instead climb up and cross to the other side using the bridge. Hidden Evidence is inside the cave.
At the bridge where you can't cross over the barbed wire, drop to your right, and shimmy to the right until you can climb up the bridge again. There is an RTL line. Move up the line, right of the bridge. Drop down at the ledge and move ahead. Hidden evidence is inside the lower cave.
From the evidence above (#4), climb up, and walk to the opposite area of the fourth evidence. You should see some kind of small curve wall. Around that area look really close / walk, because the hidden evidence is lying in the middle of the ground, but due to its color, it's hard to spot.