When they look out of a window and it's dark outside they would not be able to see a thing! You would have to switch the lights off in the room.
And with a potentially dangerous situation going on, there's a knock at the front door. So they go and open the door. Thus allowing the murderer, stalker, nutcase to enter and do the very thing they had been trying to avoid happening.
Halfway through watching Treason on NF and it's quite good but WHY - when someone is trying to kill you - don't they close their curtains after dark ???????????
It's the same when a beautiful woman is being stalked and she hears a noise in the garden, so she goes running outside to see what it is!!!!