Hawk sighting

It snowed today in North Chicago and some sort of hawk or eagle took refuge on the side of our building. Everyone was really excited to see it. We all crept into the room with its windo and we were able to get close to the window. It didn't seem to be afraid of us at all. AFter the snow stopped, it flew away. Does anyone know what type of bird this is?
Update: It is a mature red tailed hawk. Note the distinctive chest band (second and third picture down.) Thanks Illinois Raptor Center