You file an open records request with the agency that is in possession of the police vehicle camera.  Most agencies now have information listed on their websites of who to contact to make these types of requests.  Some agencies require you to use their specific form.  If they don't have a form, you still need to submit the request in writing.  You need to make sure you specify what you are looking for and the time frame.  If your request is too broad to be effective, they can avoid compliance with the request. If you have an ongoing criminal case, you can simply file a motion for a copy of the patrol video as you would have the right to view the evidence against you.