A lot of local animal controls will provide traps either free (with a deposit) or at very low rental cost to help you trap. They can also help you understand exactly what the law says.
Personally, I would not have any problems with trapping and taking to animal control. While I'm not into killing animals in general, I would also not have any problems shooting them with a bb gun. Just check with animal control first, to make sure you are within your rights of protecting your animals (usually that is the case - it's OK to shoot if they are on your property and molesting your animals/kids/grandmother/etc)
I don't understand where people who would never let their dogs run loose and bother other people have no problems letting their cats run wherever they want to go and to breed and kill at will. Cats are predators, plain and simple, and if there are cats, they are a risk to your chickens, especially bantys or young ones.
Good luck with your traps... but unless those cats are really hungry/feral, I wouldn't bet on catching them. If these are fat cats, they probably belong to someone who is feeding them very well, and your chickens were simply a trigger to their hunting instinct, rather than a meal to them. No self respecting cat I ever knew would go into a trap unless they were absolutely starving.
Susan