Pretty good advice from Uncle Nicky - to keep quiet about it whatever you do.In some states, it's not legal to shoot cats, so I would check your laws to be sure. A while back, I read where a guy got a pretty stiff fine for killing a cat here in Vermont.
The issue of cats being allowed to run loose - either pets or feral - is a very touchy one, and people on both sides tend to have very strong opinions and these have led to some awful flame wars on different web sites.