I would have killed the predator without batting an eye. If it were lucky enough to make it off my property when I caught it in the act, a live trap would be out before nightfall. Then I would have disposed of it discreetly & with much glee.
I like cats, better than dogs infact---as pets. Once they begin to harm livestock, however, they are no longer pets in my eyes, now they are pests.
The animal was lucky you chose a paintball gun. If the owner can't see fit to protect their "pet", then you have no choice but to rid yourself of a problem however you see fit.
I don't know if there is a leash law where you live, here it is county wide, and includes cats. Maybe you could call animal control and have them set out a trap. That way you would be (without question) on the right side of the law. The cat would be tagged a nuisance animal, and the owners would have to pay to get it out of "jail"....if they cared that much. You would be covered in the event you are forced to kill it.