Even if you are uninsured, you always need contact the police immediately. They will determine what extent they need to be involved. Even though you did not contact them at the time, you should still contact them immediately. They will possibly be able to determine fault in the accident. They may be able to help you contact the other party if you are unable to reach him or verify his insurance through USAA. Speaking of USAA, if he was insured through them, you will want to try to contact their national headquarters to see if the other party has insurance through them.
Remember, you can get free auto insurance quotes by clicking here.