You are going a bit in and out of this level. The secrets is in the final part. You have to shoot two red lights out, to make a heavy beam swing out of your way. Go to the first bend in the corridor, turn right and shoot the crack in the wall - there is the first secret.

Call this a 'secret' again! Wipe out the big guy, jump on top of the demolition charge, to the top of the crates. Hrm.