In my freshman year, a squirrel was murdered outside of my dorm building. The perpetrator was a bird of prey of some fashion. It gathered onlookers as it slowly consumed its victim, stopping at the halfway point, once the corpse was light enough, to carry the remains up into a tree for a safer meal. It was not especially large, and it struggled to carry even half of a squirrel into the lowest branch of a nearby oak, but it had efficiently and quickly killed its prey with a large set of talons.
I never looked into its identity then, and the pictures of it are long gone, but I think I’ve narrowed it down to two possibilities; A red-shouldered hawk or a red-tailed hawk. The former only occasionally prey on tree squirrels, while the latter do so far more often. This is probably due to their respective sizes – red-shouldered hawks seem to prefer prey that is smaller than them, and eastern grey squirrels such as our campus’ famed black squirrels can easily grow to match their weight. Red-tails tend to outweigh tree squirrels by a comfortable margin, but they also seem to prefer ground squirrels to their arboreal cousins.
Ultimately, based on their native ranges, I would guess it was a young red-tailed hawk. Red-shoulders only spend their summers in this area, but red-tails will often spend their lives here.