I live in the area as well and have talked with police about it.

There are a couple of major problems unique to the area. One is that the homeless shelter attracts people who, well, aren't really right in the head. The shelter will not accept just anyone who shows up (yes, they have standards too) and turns away people for various reasons, who then wander wherever.

The other problem is that as you pointed out you are next door to the police HQ. And also Arlington County Jail. The jail (I got this straight from their public affairs liaison) can and does release inmates who are qualified for release at any time, day or night.

Although I'm unaware of anyone suffering serious physical harm from one of these people, it creates a situation where it's easy for a serial groper to get away with stuff like this, or with casual property theft from a garage. My advice is to always keep aware of your surroundings, people like this tend to avoid alert pedestrians and instead prey on the unwary.