Following the cutscene, blow up three trip wires, pass through, and then kill two guys before walking up some stairs. A sniper from upstairs scans the next hallway, so wait until he's done with his ...

Walk straight, turn left into the room, and read the note on the dead guy's back. Nice. Back into the main room, wait until a thug turns the corner and shoot the two cans of gasoline to dust him off.