Where Did This Blood Come From?

My neighbor called our apartment complex security and told them, "There's blood all over the outside of my window air-conditioning unit." He lives on the 11th floor, so this was odd. They sent a guy. He walked in, looked at the A/C unit, gasped, and got on his walkie-talkie, "Yeah, it's really blood." Minutes later five security guards were in the living room taking photos on their phone. Did someone leap from the roof and hit his A/C unit on the way down? Is this strange blood the calling card of a new mass murderer indicating that "he'll be back for you" in a few days? Well, in the end we figured out that a hawk killed a squirrel or mouse and ate it on the A/C unit, but it was fun guessing.