thanks.
its was on the same level, and i can now pinpoint its source.
its the sniper, still dont know exactly why.
when he reaches a certain "accuracy level" he flashes a strong beam of red light (you can hear it too), there is one sniper inside the room at the end of the first hall and one at the end of the long corridor. You can even see the black stuff coming out at the height of a character.
its one of those things that if I was making a pixelated horror game I couldnt make it work if I tried, and here it is, some black misterious fog chasing the player around, eheh.