The way I understood the description was that Hailey's door was shut, but she could hear him and see the shadow of his feet, so she knew he was there. Not that her door was open and he was looking. I could be wrong, but I was pretty sure about the "shadow" thing.
Salem
You are probably right about that Salem. Here's the NG transcript...
GRACE: Ms. Jones -- Ms. Jones, your theory that the live-in boyfriend sexually attacked the little girl and that he killed her when she threatened to tell -- what do you base that on?
JONES: Because Hailey had told me (INAUDIBLE) him been living there in the past that he would walk around at nighttime, and the hall light would be on, and she could see his shadow at her door, at the foot of the door. She could see his legs at the foot of the door, just at her door, just standing there. And it scared her. And I don`t know, things just don`t add up that Monday. Why would he leave his job? He didn`t quit, he just left his job.
GRACE: Well, hold on, Billie. Hold on, Billie Dunn. What was she afraid of? What specifically would she say, Ms. Jones?
JONES: That she was afraid of him walking around at night. She said that he`d go in the bathroom and he`d use Billie`s phone and talk to people and then come out and just stand by her door. She said he -- she was just afraid of him. At this time, she was only, like, 11.
GRACE: Did she tell you anything other than him standing by her bedroom door at night?
JONES: No. She said he never tried any advances toward her or anything and...
GRACE: Did you ask her?
JONES: Yes, ma`am. I asked her a lot if he ever tried anything to her. And I told her, I said, If he ever tries anything, you tell your mom and your dad. I said, Don`t -- I said, He can`t -- he`s not going to get away with it, Hailey, if he ever touches you in any way.
GRACE: And what would she say? When you would tell her that, what would she say?
JONES: She said that she would and everything. And the last couple of months, I hadn`t seen her very much because her dad moved over to Colorado City. And she usually spends the night, sometimes the weekend with me, and I hadn`t seen her that much. But she always called me, almost every day.
http://transcripts.cnn.com/TRANSCRIPTS/1101/13/ng.01.html
I must have missed the part about CD only moving to Colorado City in the last couple of months. Sounds like HD was spending a lot of time sleeping at grandma's before that move and then at CD's new place I suppose. Perhaps he was living with his Mom in Snyder before the move?