So it was a hawk after all. I see these near our place, usually hanging out by the first (i.e. south) Donghe bridge, but I've never seen one close enough to identify its markings. They tend to fly much closer to the ground and for shorter periods. He must have been perching in a nearby tree.

What an experience. It beats the heck out of sitting around watching TV. How many times do you catch a hawk in one lifetime?