How did the murderer sneak into the room?

The scene is when Lattimore and Lavin are in the hotel room. He's in the bathroom and she's lit up a cigarette by the rear door. While they converse we see someone is outside. A few seconds later she sits down in the chair by the door. We see the killer putting on gloves outside. Then, a few seconds later she looks over and sees that the door is cracked open, then we see the necktie being picked up by the killer from where it has been casually laid on the sofa in the room.

She's been near the door the whole time, either standing or sitting. How did the killer get in without her seeing him? This seems like a big continuity error.