Legal Question in Real Estate Law in California

The police will view this as a civil matter that they will not want to be involved in. Unless you can show them that your ex has absolutely no basis to claim ownership of the cat they will not treat it as a criminal act. You will have to look at the divorce decree to determine who should have possession of the cat [pets are considered personal property] and if it is not clear then yo need to go back to family court to have the judge deal with that issue.

If you were formerly married and are now divorced, I agree with Mr. Shers that this will be treated as a civil matter and you might even get in trouble for making a false police report. If however by "ex" you mean a boyfriend or girlfriend rather than a spouse, you might have a better chance with the police, but be sure the circumstances resemble a theft rather than just a failure to turn over possession upon request. There are civil actions for recovery of personal property wrongfully in the possession of another -- formerly known as "replevin," such actions are now referred to as "claim and delivery" actions in the current codes. See, e.g., Code of Civil Procedure sections 511.010 et seq.