The law does not regulate who’s cat gets to go outside and where they can roam. There are some provisions for property damage or ‘nuisance’, but again, the burden will be on the owner (in this case, the OP), to prove such charges and if there are findings, the cat might be killed (i.e., euthanized).
Cat doors and/or open windows are an invitation to many different animals, e.g., cats, possums, raccoons, squirrels, etc. They are animals. They don’t know they ‘shouldn’t assume’ that they are invited in. If one chooses to provide this type of ingress/egress for their cat, one needs to accept the risk that uninvited guests may also use the ingress/egress.
My view is that when we let our cats have unsupervised access to the outdoors, we are risking their health/well being and therefore, are responsible for anything that happens to them. Why, because..they are cats and cats will be cats. Period. I can only look at/change my behavior; no one else’s (even thought I’d like to).
IMHO the responsibility is on us, as their concerned caregiver, to take the steps to ensure their safety. Hence, I have two outdoor enclosures that are secured and butted up to basement windows so my cats can go in and out 24 hours a day. They are safe from (non-family)cat attacks; dogs; cars; poisons; coyotes; and they don’t poop in my neighbors’ flower beds.
