Legal Question in Landlord & Tenant Law in California

Not much. The landlord is entitled to be paid the rent and since you live there you are stuck for the entire amount. You can try to hunt down the roommate but does he have any assets? You can screw up his credit somewhat by getting a judgment against him, which can be renewed every ten years. It will also come up when he tries to rent another place and the landlord does a credit check. You can report him to the police, but they will consider it to be such a minor crime compared to everything else they must deal with that they likely will not do anything, unless you live in an area with a very low crime rate.

Tell the landlord what happened and see if something can be worked out. Remember for the future that you can never be sure who you can trust, especially with money.