Can I call the cops on a klepto NPC?

Although represented in-game as a trait, kleptomania is a disease (disorder). You can't cure a disease by punishing someone. I'm actually not sure if inactive sims even keep the items they grab that way; homeless NPCs like maids and babysitters certainly cannot because they have no family inventory.

I can see though where one might not want this element in their game. The trait can be swapped out in favor of others. Those using mods will have an easier time of this -- NRaas MasterController would be much more efficient in finding sims with this trait and doing the swap than having to bring everyone in town into CAS, and StoryProgression can be used to disallow the trait townwide or on certain classes (castes) of sims as desired.

You can't call the police to arrest them. If you do they will fine you.

@IreneSwift Well, that sucks. I'm glad that the MasterController and StoryProgression can help with that, at least.

@Zei - The title of your thread gave me a chuckle! While I don't think the Klepto's should be 'punished' for doing something they cannot control, I do think the Sims team should have wrote in an option which would allow your Sim to ask for their object back before they (the Klepto) leaves the property. After all, if you are actively playing with a Sim with this trait, they have the option to 'return' what was taken (although, I've never actually seen any items returned).

The way the game was written, it treats it's players (us Simmers) very 'unfairly' and in ways which can be stress inducing; especially when an event which is small in scope, 'should' have a simple solution, yet offers none. IreneSwift is correct. If you were to call the police your Sim would have been charged 500 simoleons for making a false report.

The thing to remember about Kleptos is they cannot (or are not suppose to) steal anything if there are other Sims around. The best you can do outside of adding mods is 'Klepto-proof' your home by keeping all snatch-able items behind locked doors and putting cheaper furnishings in guest areas but enhancing the space with items which offer environment boosts so your guest sleep well.