Employee gets degraded from colleague status to stalking status

After calling and leaving several messages on a colleague’s voice-mail and email, walking by and peering in window, stalking employee reverted to calling the employee who sits across from stalked colleague’s office to find out if she was in her office. Employee taking call from stalker was very tempted to respond by staying that stalked colleague is actually hiding behind the door only to see if stalker employee would go check stalked colleague’s office window again and/or say that she did notice woman in office looked at the phone a few times when it rang and blatantly didn't answer before taking her hiding position. Stalker continues to peer through window and stand in front of it for minutes at a time before moving on to attempt work.