A Greusome Feast

Yesterday afternoon I watched from my kitchen window while this bird tore at the flesh of an unidentified rodent that probably made its home in my back yard.

In the past we have seen Coopers Hawks in our backyard and assumed that they nested near our house.  Something makes me think this isn't a Coopers Hawk, though.  It seemed smaller and the feathers on its back were positively blueish.  Possibly a Peregrine Falcon?  Maybe that's just wishful thinking.  It could have been a smaller Cooper because I think the males are supposed to be smaller than the females, but that still doesn't explain the feathers.  If you have a suggestion, I would be honored if you would enlighten me.  I am only a very ammature birdwatcher.