The one shooting in D.C. was just barely inside D.C., just south of the boundary with Montgomery County, MD. In fact, as I determined from personal observation on Saturday, the sniper may have shot from inside MD: from the roof and upper stories of the Ramada Inn three or four blocks of the place where the victim was hit, you would have had a clear line of sight to the victim -- and the Ramada Inn is in Montgomery County, MD.
I'm not convinced the killer is shooting from hotel balconies/rooftops; I'm inclined to think the fact that many of the shooting locations are at major exits off major interestates means there will be an abundance of both gas stations and motels/hotels clustered around. But I think all options should be turned over and examined, so the rooftop sniping is as good a guess as a shooter-on-the-ground or shooter-in-the-van theory.