My ex-girlfriend continues to threaten me with harassment.

My ex-girlfriend continues to threaten me with harassment.
Since we broke up I have a new girlfriend. I have contacted her multiple times to try to get her to pick up her remaining items here, I even offered to leave them outside of the house so she could get them without talking to me.
Recently she saw me outside of her work (a 34 storey office tower). I have many contacts and friends who work in the building and again threatened to allege harassment. I was actually waiting for a friend who works in her office. I have many contacts in that office because I actually got her that job.
I have never sent a message that has been threatening or angry in any way. Once she started posting posters up about me all over town, threatening to punch me in the face and cut off my ***** and break into my house I created a police file in case she escalated from idle threats to actual violence.
My concern is not that I want anything but a cordial relationship with her. Rather my concern is that I cannot completely avoid that building, just because on the off chance she comes outside or downstairs sees me and alleges harassment. I have many contacts in the office where I got her a job and its not unlikely that I may have meetings with old contacts or even start working there again.
I never contact her at work over anything personal by phone email or other means. I even try to avoid sending her any personal emails or text messages during business hours.
I am wondering what I should do in order to feel secure in accessing my contacts or even being outside of that building (its a huge financial tower in the financial district). I could understand if I went to reception and asked for her directly about a personal matter that this would be a problem - but having a cigarette outside the building waiting for a text from a friend who works inside?
I want to take precautions and know my rights. This 21 year old bumpkin should not be able to prohibit me from going near a building where I have many contacts on many floors after 25 years in the business. I myself worked in that building on three different floors over an aggregate 7 years.
Any advice?