Bobcats, raccoon, 'possums, foxes and skunks can all climb just like cats! We had a 5' cinder block fence in San Antonio. We would put a harness on Fat Cat and let her out in the back yard occasionally. One day, she was frantic to get in the house, so we went to oblige her (as everyone should with cats - they think they are superior beings, you know) and there was a huge skunk in our back yard! We all stood inside the house and watched him climb straight up and over that fence without the slightest problem or hesitation. We were amazed!
Whatever got your hen and upset your flock, chicken curious, is sure to be back now that they know your chickens are there and tasted blood. I'm a pretty good shot with a .22 rifle, but would sure hesitate to use one even out at our pens. There are neighbors closer than the range of a .22 bullet in case I missed...a 410 shotgun, however, would be just the ticket. You might pepper a neighbor's house, but after that distance, there wouldn't be much behind those pellets.
Best of luck to you,
Brie