Idiotic use of a firearm. My guess is that the guy has other issues and this is a timely spotlight on him.
The firearm was a BB gun. The cats were probably a nuisance to him so he shot one. All the cats on my dead end street know to stay out of my back yard. They probably heard about all the squirrels and raccoons that were felled by .177 hollow point lead pellets at 1,020 f.p.s. courtesy of Gamo. There was a big gray Tom that used to sit just outside of the rear sliding glass door at night to taunt my dog when he was still alive. About the third time that happened I cocked the Gamo and the pellet just missed the cat who was lucky it was dark. I never saw that cat in the back yard again.
According to another poster it was a BB gun and not a firearm. That makes sense because I would imagine shooting a firearm in a apartment complex would get you charged with felony criminal recklessness with a firearm.