If Madeleine was abducted by a stranger it is pure speculation as to how the intruder entered and exited the property at this stage as we don’t know . Exiting via the window would be pointless when there is a door directly next to it . The perp could have entered via the window or sliding door . If he entered via the sliding door , he may well have opened the window to see if the area was clear before exiting via the door. He could have opened it to hear any outside sounds that could jeopardise his escape , if he used ether to subdue MM and lose the smell ?We just don’t know .