There are several dark places without civilians. You just have to circle around to find them. That mission was actually easy, once you know their routes.
I was trying to avoid the civilians entirely,my mistake.You only have to interrogate the men out of the view of the civilians.
They CAN actually see you through walls later in the game, using a gadget.
The elite guards that is.
i was referring to the grunts my bad they seem to have super human sight/hearing which is annoying. they dont have the sonic glasses but still see me right through the wall even when im not moving or making any noise