This poor photo in low light shows what I presume to be the same young accipiter shown in a better picture taken the next day in sunlight at http://www.pbase.com/image/105915772. I thought the head size/shape in this one looked right for Sharp-shinned, and the bird looked notably small to me in the field in both sightings, though without any nearby bird for comparison. The tail tip looked square in the other picture; in this one it unhelpfully looks neither square (Sharpie) nor curved (Cooper's), but pointed.