The way to handle this would have been to call the County Sheriff and plead your case before they even left the scene. By all rights, if LE is stealing what is yours, you should be able to defend yourself using any means necessary. YES, that does include a gun. Cops have a gun and they would kill you if necessary to enforce a regulation. Citizens have the right to enforce their right to property and due process.
In this case, they were not "stealing" the car. They impounded it for evidence, which is perfectly legal, standard operating procedure, and would be held up in court.