Greg, I don't condone shooting cats (with bb guns, pellet guns, 22s or otherwise) for the fun of it or the sake of it. Cruelty to cats (or any other animal, domestic or otherwise) should not be tolerated.
If your coworker's cat was shot while "roaming" around, it sounds like he needs to address the issue. BUT if his cat was shot while on HIS property, the shooter should be prosecuted. I mean that. The topic of this discussion was directed at a neighbor's cat on the OP's property. I've noticed (at multiple places where I've lived) that cat owners simply allow (or seem to think there is no problem with) their cats to roam. They say "That is what cats do." I disagree. Just as I disagree that dogs incessant barking is "What dogs do." (And I am a dog owner and lover.) Just like smokers that throw cigarette butts on the ground and don't think it is littering (or a fire hazard presumably). Sorry, I DO take issue with other people's lack of responsibility...especially when it affects others. If you are going to smoke, dispose of your butts properly. If you are going to own a dog, don't let it sit outside and bark for hours on end. If you own a cat, don't let it roam off your property. If you can't do those simple things, you shouldn't smoke, own a dog, or own a cat.