[Extremely Extreme Extremist]

Looks like a shadow from someone walking outside the window to me.

There's no adjacent windows in that room.

[traderrob6]

Maybe not directly adjacent but kitty corner. Light and shadow can play some strange tricks.

[Dixie Yooper]

There's no adjacent windows in that room.

All it takes is a light source and someone walking in front of it. Since the room is at the end of a long hallway, you have no idea where the light is in that room, and no idea how many people could have been all over the house during this filming. He's still dead and is going to stay that way.

[bird4four4]

It looks to me like there is someone in the far room. He casts a shadow on the back wall. Then the floor is highly reflective (see the fireplace) so the shadow appears to cover the back wall and the floor in the hallway. Causing the appearance the the shadow base is in the hall way but it is a reflection of the top of the shadow.